DC free code design with state dependent mapping

ABSTRACT

A codeword for use in a communication channel is provided. A first segment of the codeword includes a plurality of bits having a running digital sum (RDS) and a second segment includes a plurality of bits based on the RDS of the first segment.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims priority of U.S. patent application Ser. No. 10/395,495, filed Mar. 24, 2003, which claims the benefit of U.S. Provisional Application 60/409,156 filed on Sep. 9, 2002 for inventor Kinhing P. Tsang and entitled DC FREE CODE DESIGN WITH STATE DEPENDENT MAPPING, the contents of which are both hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to communicating digital data through a communication channel. In particular, the present invention relates to encoding and decoding techniques for DC free codes.

BACKGROUND OF THE INVENTION

In the field of digital communications, digital information is typically prepared for transmission through a channel by encoding it. The encoded data is then used to modulate a transmission to the channel. A transmission received from the channel is then typically demodulated and decoded to recover the original information.

The encoding of the digital data serves to improve communication performance so that the transmitted signals are less corrupted by noise, fading, or other interference associated with the channel. The term “channel” can include media such as transmission lines, wireless communication and information storage devices such as magnetic disc drives. In the case of information storage devices, the signal is stored in the channel for a period of time before it is accessed or received. Encoding can reduce the probability of noise being introduced into a recovered digital signal when the encoding is adapted to the known characteristics of the data and its interaction with known noise characteristics of a communication channel.

In typical encoding arrangements, data words of m data bits are encoded into larger code words of n code bits, and the ratio m/n is known as the code rate of the encoding arrangement. Decreasing the code rate improves decoding and can also improve error correction, however, a decreased code rate also increases energy consumption and slows communication.

Further, it is often desirable for encoded channel sequences to have a spectral null at zero frequency. Such sequences are said to be DC free and particularly found to enhance the performance in perpendicular magnetic recording. Given a sequence of binary digits, wherein a binary digit “1” is plus one (+1) and a binary “0” is minus one (−1), the sequence will be DC free if a running digital sum of the sequence is bounded. The running digital sum is the sum of all values in a sequence. When the variation of the running digital sum is kept to a small value, it is known to have a tight or small bound. A tighter bound improves the performance of the channel.

There is a need to provide improved DC free coding techniques that reduce the probability of noise being introduced to the system and have optimal code rates. Various embodiments of the present invention address these problems, and offer other advantages over the prior art.

SUMMARY OF THE INVENTION

A codeword for use in a communication channel is provided. A first segment of the codeword includes a plurality of bits having a running digital sum (RDS) and a second segment includes a plurality of bits based on the RDS of the first segment.

Another embodiment includes a codeword representing an encoded data word for use in a system. The codeword includes a first segment representing a first fragment of the user data word and a second segment representing a second fragment of the user data word. The first segment and the second segment representing a state value for the system.

Other features and benefits that characterize embodiments of the present invention will be apparent upon reading the following detailed description and review of the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a disc drive.

FIG. 2 is a flow diagram of a method of encoding information according to the present invention.

FIG. 3 is a block diagram of an encoder.

FIG. 4 is a block diagram of an encoder input circuit.

FIG. 5 is a block diagram of a first encoder circuit.

FIG. 6 is a block diagram of a second encoder circuit.

FIG. 7 is a block diagram of a third encoder circuit.

FIG. 8 is a block diagram of an encoder for generating a first segment of a code word.

FIG. 9 is a block diagram of an encoder for generating a second segment of a code word.

FIG. 10 is a block diagram of an encoder output circuit.

FIG. 11 is a flow diagram of a method of decoding digital information.

FIG. 12 is a block diagram of a decoder.

FIG. 13 is a block diagram of a decoder input circuit.

FIG. 14 is a block diagram of a decoder for decoding a first segment of a code word.

FIG. 15 is a block diagram of a decoder for decoding a second segment of a code word.

FIG. 16 is a block diagram of a decoder output circuit.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 is a perspective view of a magnetic disc drive 100 in which the present invention is useful. Disc drive 100 communicates with a host system 101 and includes a housing with a base 102 and a top cover (not shown). Disc drive 100 further includes a disc pack 106, which is mounted on a spindle motor (not shown), by a disc clamp 108. Disc pack 106 includes a plurality of individual discs, which are mounted for co-rotation about central axis 109. Each disc surface has an associated head, which is mounted to disc drive 100 for communication with the disc surface. In the example shown in FIG. 1, heads 110 are supported by suspensions 112 which are in turn attached to track accessing arms 114 of an actuator 116. The actuator shown in FIG. 1 is of the type known as a rotary moving coil actuator and includes a voice coil motor (VCM), shown generally at 118. Voice coil motor 118 rotates actuator 116 with its attached heads 110 about a pivot shaft 120 to position heads 110 over a desired data track along an arcuate patch 122 between a disc inner diameter 124 and a disc outer diameter 126. Voice coil motor 118 operates under control of internal circuitry 128.

The heads 110 and rotating disc pack 106 form a communication channel that can receive digital data and reproduce the digital data at a later time. Write circuitry within internal circuitry 128 receives data, typically from a digital computer, and then encodes data in code words adapted to the communication channel. The encoded data is then used to modulate a write current provided to a write transducer in the head 110. The write transducer and the head 110 causes successive code words to be encoded on a magnetic layer on disc pack 106. At a later time, a read transducer in the head recovers the successive code words from the magnetic layer as a serial modulated read signal. Read circuitry within internal circuitry 128 demodulates the read signal into successive parallel code words. The demodulated code words are then decoded by decoder circuitry within circuitry 128, which recovers the digital data for use, by host system 101, at a later time.

In order to encode data that is written onto a magnetic layer on disc pack 106, a method according to the present invention is used. According to one embodiment of the present invention, a 19-bit word of user data is encoded into a 20-bit code word. In order to generate the 20-bit code word, the 19-bit data word is broken down into smaller fragments. The fragments are rearranged and mapped into two 10-bit segments according to a lookup table and a mapping table. In one embodiment, a goal of the method is to maintain the running digital sum of the system within a selected range of +/−4, calculated after each 20-bit code word. The selected range represents a bound on the running digital sum of the system. Maintaining the running sum within the selected range improves the performance of disc drive 100. Upon decoding of the code word, the code word is evaluated in order to determine a state value. Using the state value, the code word can be decoded using the state value to render the sequence of user bits.

FIG. 2 illustrates a flow diagram of a method 200 of encoding information according to the present invention. According to method 200, a 19-bit data word is received at step 202. At step 204, the method 200 accesses a current state value that has been calculated after each code word that is generated. The current state is the running digital sum of the system. The initial state is calculated as zero. Depending on the current state, the 19-bit data word is broken up into three fragments according to a lookup table at step 206. The assembly and format of the lookup table is discussed below. Next, at step 208, a ‘g’ group and an ‘h’ group is selected based on the first fragment as determined in step 206. These groups are chosen in order to maintain the running digital sum within a range of +/−4. Once the respective groups are obtained, the second fragment is mapped into a ‘g’ group 10-bit segment at step 210. The mapping is performed according to a mapping table as discussed below. In step 212, the third fragment is mapped into an ‘h’ group 10-bit segment according to a mapping table. The ‘g’ group and ‘h’ group segments are then combined, at step 214, to form a 20-bit code word that maintains the running digital sum of the system within +/−4. The code word is output, for example to a disc, at step 216.

In order to generate the lookup table, it is important to investigate the running digital sums for 20-bit code words. By separating 20-bit code words into 10-bit segments, the design of a rate 19/20 DC free code is simplified. For a given a 10 bit pattern, the pattern may have a running digital sum of −10, −8, −6, −4, −2, −0, 2, 4, 6, 8 or 10. Table 1 shows 10 bit patterns grouped according to their respective digital sums. The groups having running digital sums of 0, 2, 4, 6 and 8 are shown. Since the running digital sums of −2, −4, −6 and −8 are merely the inverse of the corresponding patterns with the positive running digital sum, only the groups with a positive running digital sum are shown. The patterns having running digital sums of 10 and −10 are not used. The table shows the 10-bit patterns in hexadecimal. TABLE 1 A Grouping Table that groups 10-bit segments according to their respective running digital sums. Group gb: There are 252 10-bit patterns with RDS = 0 01F 02F 037 03B 03D 03E 04F 057 05B 05D 05E 067 06B 06D 06E 073 075 076 079 07A 07C 08F 097 09B 09D 09E 0A7 0AB 0AD 0AE 0B3 0B5 0B6 0B9 0BA 0BC 0C7 0CB 0CD 0CE 0D3 0D5 0D6 0D9 0DA 0DC 0E3 0E5 0E6 0E9 0EA 0EC 0F1 0F2 0F4 0F8 10F 117 11B 11D 11E 127 12B 12D 12E 133 135 136 139 13A 13C 147 14B 14D 14E 153 155 156 159 15A 15C 163 165 166 169 16A 16C 171 172 174 178 187 18B 18D 18E 193 195 196 199 19A 19C 1A3 1A5 1A6 1A9 1AA 1AC 1B1 1B2 1B4 1B8 1C3 1C5 1C6 1C9 1CA 1CC 1D1 1D2 1D4 1D8 1E1 1E2 1E4 1E8 1F0 20F 217 21B 21D 21E 227 22B 22D 22E 233 235 236 239 23A 23C 247 24B 24D 24E 253 255 256 259 25A 25C 263 265 266 269 26A 26C 271 272 274 278 287 28B 28D 28E 293 295 296 299 29A 29C 2A3 2A5 2A6 2A9 2AA 2AC 2B1 2B2 2B4 2B8 2C3 2C5 2C6 2C9 2CA 2CC 2D1 2D2 2D4 2D8 2E1 2E2 2E4 2E8 2F0 307 30B 30D 30E 313 315 316 319 31A 31C 323 325 326 329 32A 32C 331 332 334 338 343 345 346 349 34A 34C 351 352 354 358 361 362 364 368 370 383 385 386 389 38A 38C 391 392 394 398 3A1 3A2 3A4 3A8 3B0 3C1 3C2 3C4 3C8 3D0 3E0 Group gc: There are 210 10-bit patterns with RDS = +2 03F 05F 06F 077 07B 07D 07E 09F 0AF 0B7 0BB 0BD 0BE 0CF 0D7 0DB 0DD 0DE 0E7 0EB 0ED 0EE 0F3 0F5 0F6 0F9 0FA 0FC 11F 12F 137 13B 13D 13E 14F 157 15B 15D 15E 167 16B 16D 16E 173 175 176 179 17A 17C 18F 197 19B 19D 19E 1A7 1AB 1AD 1AE 1B3 1B5 1B6 1B9 1BA 1BC 1C7 1CB 1CD 1CE 1D3 1D5 1D6 1D9 1DA 1DC 1E3 1E5 1E6 1E9 1EA 1EC 1F1 1F2 1F4 1F8 21F 22F 237 23B 23D 23E 24F 257 25B 25D 25E 267 26B 26D 26E 273 275 276 279 27A 27C 28F 297 29B 29D 29E 2A7 2AB 2AD 2AE 2B3 2B5 2B6 2B9 2BA 2BC 2C7 2CB 2CD 2CE 2D3 2D5 2D6 2D9 2DA 2DC 2E3 2E5 2E6 2E9 2EA 2EC 2F1 2F2 2F4 2F8 30F 317 31B 31D 31E 327 32B 32D 32E 333 335 336 339 33A 33C 347 34B 34D 34E 353 355 356 359 35A 35C 363 365 366 369 36A 36C 371 372 374 378 387 38B 38D 38E 393 395 396 399 39A 39C 3A3 3A5 3A6 3A9 3AA 3AC 3B1 3B2 3B4 3B8 3C3 3C5 3C6 3C9 3CA 3CC 3D1 3D2 3D4 3D8 3E1 3E2 3E4 3E8 3F0 Group gd: There are 120 10-bit patterns with RDS = +4 07F 0BF 0DF 0EF 0F7 0FB 0FD 0FE 13F 15F 16F 177 17B 17D 17E 19F 1AF 1B7 1BB 1BD 1BE 1CF 1D7 1DB 1DD 1DE 1E7 1EB 1ED 1EE 1F3 1F5 1F6 1F9 1FA 1FC 23F 25F 26F 277 27B 27D 27E 29F 2AF 2B7 2BB 2BD 2BE 2CF 2D7 2DB 2DD 2DE 2E7 2EB 2ED 2EE 2F3 2F5 2F6 2F9 2FA 2FC 31F 32F 337 33B 33D 33E 34F 357 35B 35D 35E 367 36B 36D 36E 373 375 376 379 37A 37C 38F 397 39B 39D 39E 3A7 3AB 3AD 3AE 3B3 3B5 3B6 3B9 3BA 3BC 3C7 3CB 3CD 3CE 3D3 3D5 3D6 3D9 3DA 3DC 3E3 3E5 3E6 3E9 3EA 3EC 3F1 3F2 3F4 3F8 Group ge: There are 45 10-bit patterns with RDS = +6 0FF 17F 1BF 1DF 1EF 1F7 1FB 1FD 1FE 27F 2BF 2DF 2EF 2F7 2FB 2FD 2FE 33F 35F 36F 377 37B 37D 37E 39F 3AF 3B7 3BB 3BD 3BE 3CF 3D7 3DB 3DD 3DE 3E7 3EB 3ED 3EE 3F3 3F5 3F6 3F9 3FA 3FC Group gf: There are 10 10-bit patterns with RDS = +8 1FF 2FF 37F 3BF 3DF 3EF 3F7 3FB 3FD 3FE

Each of the groups in Table 1 is further divided into subgroups of various sizes. The various subgroups map bits of user fragments determined in step 206, depending on the size of the user data, into a 10-bit code word. For example, a user data fragment of 7 bits is mapped into a 7-bit subgroup, for example subgroup gb7. This group will be utilized when the first fragment has a length of 7 bits. Group gb is divided into subgroups gb7, gb6, gb5 gb4 gb3 and gb2 with sizes of 128=2⁷, 64=2⁶, 32=2⁵, 16=2⁴, 8=2³ and 4=2² respectively. Group gc is divided into subgroups gc7, gc6, gc4 and gc1 with sizes of 128=2⁷, 64=2⁶, 16=2⁴ and 2=2¹ respectively. Group gd is divided into subgroups gd6, gd5, gd4 and gd3 with sizes of 64=2⁶, 32=2⁵, 16=2⁴ and 8=2³ respectively. Group ge is divided into subgroups ge5 and ge3 with sizes of 32=2⁵ and 8=2³ respectively. Group gf is divided into subgroups gf3 and gf1 with sizes of 8=2³ and 2=2¹ respectively. The size of each subgroup is of a size 2^(m), which allows mapping of user data fragments of size m bits. Table 2 shows each of the various subgroups. In the table, the mapping is shown in the form “xxx:yyy”, wherein “xxx” is a user data fragment that is mapped into a 10-bit code word “yyy”. The values in the table are expressed in hexadecimal. TABLE 2 Mapping Table of user fragments into ‘g’ group words. Subgroup gb7: (mapping of 7-bit data word into 10-bit code word) 000:21B 001:233 002:235 003:236 004:22B 005:239 006:23A 007:23C 008:24B 009:253 00A:255 00B:256 00C:28B 00D:259 00E:25A 00F:25C 010:21D 011:263 012:265 013:266 014:22D 015:269 016:26A 017:26C 018:24D 019:293 01A:295 01B:296 01C:28D 01D:299 01E:29A 01F:29C 020:21E 021:2A3 022:2A5 023:2A6 024:22E 025:2A9 026:2AA 027:2AC 028:24E 029:2C3 02A:2C5 02B:2C6 02C:28E 02D:2C9 02E:2CA 02F:2CC 030:271 031:2B1 032:2D1 033:2E1 034:272 035:2B2 036:2D2 037:2E2 038:274 039:2B4 03A:2D4 03B:2E4 03C:278 03D:2B8 03E:2D8 03F:2E8 040:11B 041:133 042:135 043:136 044:12B 045:139 046:13A 047:13C 048:14B 049:153 04A:155 04B:156 04C:18B 04D:159 04E:15A 04F:15C 050:11D 051:163 052:165 053:166 054:12D 055:169 056:16A 057:16C 058:14D 059:193 05A:195 05B:196 05C:18D 05D:199 05E:19A 05F:19C 060:11E 061:1A3 062:1A5 063:1A6 064:12E 065:1A9 066:1AA 067:1AC 068:14E 069:1C3 06A:1C5 06B:1C6 06C:18E 06D:1C9 06E:1CA 06F:1CC 070:171 071:1B1 072:1D1 073:1E1 074:172 075:1B2 076:1D2 077:1E2 078:174 079:1B4 07A:1D4 07B:1E4 07C:178 07D:1B8 07E:1D8 07F:1E8 Subgroup gb6: (mapping of 6-bit data word into 10-bit code word) 000:331 001:313 002:315 003:316 004:332 005:319 006:31A 007:31C 008:334 009:323 00A:325 00B:326 00C:338 00D:329 00E:32A 00F:32C 010:3C1 011:343 012:345 013:346 014:3C2 015:349 016:34A 017:34C 018:3C4 019:383 01A:385 01B:386 01C:3C8 01D:389 01E:38A 01F:38C 020:0CE 021:0EC 022:0EA 023:0E9 024:0CD 025:0E6 026:0E5 027:0E3 028:0CB 029:0DC 02A:0DA 02B:0D9 02C:0C7 02D:0D6 02E:0D5 02F:0D3 030:03E 031:0BC 032:0BA 033:0B9 034:03D 035:0B6 036:0B5 037:0B3 038:03B 039:07C 03A:07A 03B:079 03C:037 03D:076 03E:075 03F:073 Subgroup gb5: (mapping of 5-bit data word into 10-bit code word) 000:351 001:352 002:354 003:358 004:361 005:362 006:364 007:368 008:391 009:392 00A:394 00B:398 00C:3A1 00D:3A2 00E:3A4 00F:3A8 010:0AE 011:0AD 012:0AB 013:0A7 014:09E 015:09D 016:09B 017:097 018:06E 019:06D 01A:06B 01B:067 01C:05E 01D:05D 01E:05B 01F:057 Subgroup gb4: (mapping of 4-bit data word into 10-bit code word) 000:307 001:30B 002:30D 003:30E 004:370 005:3B0 006:3D0 007:3E0 008:0F8 009:0F4 00A:0F2 00B:0F1 00C:08F 00D:04F 00E:02F 00F:01F Subgroup gb3: (mapping of 3-bit data word into 10-bit code word) 000:117 001:127 002:147 003:187 004:217 005:227 006:247 007:287 Subgroup gb2: (mapping of 2-bit data word into 10-bit code word) 000:10F 001:20F 002:1F0 003:2F0 Subgroup gc7: (mapping of 7-bit data word into 10-bit code word) 000:257 001:25B 002:25D 003:25E 004:267 005:26B 006:26D 007:26E 008:297 009:29B 00A:29D 00B:29E 00C:2A7 00D:2AB 00E:2AD 00F:2AE 010:237 011:23B 012:23D 013:23E 014:2C7 015:2CB 016:2CD 017:2CE 018:273 019:2B3 01A:2D3 01B:2E3 01C:27C 01D:2BC 01E:2DC 01F:2EC 020:275 021:2B5 022:2D5 023:2E5 024:276 025:2B6 026:2D6 027:2E6 028:279 029:2B9 02A:2D9 02B:2E9 02C:27A 02D:2BA 02E:2DA 02F:2EA 030:21F 031:22F 032:24F 033:28F 034:2F1 035:2F2 036:2F4 037:2F8 038:077 039:0B7 03A:0D7 03B:0E7 03C:07B 03D:0BB 03E:0DB 03F:0EB 040:157 041:15B 042:15D 043:15E 044:167 045:16B 046:16D 047:16E 048:197 049:19B 04A:19D 04B:19E 04C:1A7 04D:1AB 04E:1AD 04F:1AE 050:137 051:13B 052:13D 053:13E 054:1C7 055:1CB 056:1CD 057:1CE 058:173 059:1B3 05A:1D3 05B:1E3 05C:17C 05D:1BC 05E:1DC 05F:1EC 060:175 061:1B5 062:1D5 063:1E5 064:176 065:1B6 066:1D6 067:1E6 068:179 069:1B9 06A:1D9 06B:1E9 06C:17A 06D:1BA 06E:1DA 06F:1EA 070:11F 071:12F 072:14F 073:18F 074:1F1 075:1F2 076:1F4 077:1F8 078:07D 079:0BD 07A:0DD 07B:0ED 07C:07E 07D:0BE 07E:0DE 07F:0EE Subgroup gc6: (mapping of 6-bit data word into 10-bit code word) 000:31B 001:333 002:335 003:336 004:32B 005:339 006:33A 007:33C 008:34B 009:353 00A:355 00B:356 00C:38B 00D:359 00E:35A 00F:35C 010:31D 011:363 012:365 013:366 014:32D 015:369 016:36A 017:36C 018:34D 019:393 01A:395 01B:396 01C:38D 01D:399 01E:39A 01F:39C 020:31E 021:3A3 022:3A5 023:3A6 024:32E 025:3A9 026:3AA 027:3AC 028:34E 029:3C3 02A:3C5 02B:3C6 02C:38E 02D:3C9 02E:3CA 02F:3CC 030:371 031:3B1 032:3D1 033:3E1 034:372 035:3B2 036:3D2 037:3E2 038:374 039:3B4 03A:3D4 03B:3E4 03C:378 03D:3B8 03E:3D8 03F:3E8 Subgroup gc4: (mapping of 4-bit data word into 10-bit code word) 000:317 001:03F 002:05F 003:06F 004:327 005:09F 006:0AF 007:0CF 008:347 009:0F3 00A:0F5 00B:0F6 00C:387 00D:0F9 00E:0FA 00F:0FC Subgroup gc1: (mapping of 1-bit data word into 10-bit code word) 000:30F 001:3F0 Subgroup gd6: (mapping of 6-bit data word into 10-bit code word) 000:357 001:35B 002:35D 003:35E 004:367 005:36B 006:36D 007:36E 008:397 009:39B 00A:39D 00B:39E 00C:3A7 00D:3AB 00E:3AD 00F:3AE 010:337 011:33B 012:33D 013:33E 014:3C7 015:3CB 016:3CD 017:3CE 018:373 019:3B3 01A:3D3 01B:3E3 01C:37C 01D:3BC 01E:3DC 01F:3EC 020:375 021:3B5 022:3D5 023:3E5 024:376 025:3B6 026:3D6 027:3E6 028:379 029:3B9 02A:3D9 02B:3E9 02C:37A 02D:3BA 02E:3DA 02F:3EA 030:31F 031:32F 032:34F 033:38F 034:3F1 035:3F2 036:3F4 037:3F8 038:07F 039:0BF 03A:0DF 03B:0EF 03C:0F7 03D:0FB 03E:0FD 03F:0FE Subgroup gd5: (mapping of 5-bit data word into 10-bit code word) 000:277 001:2B7 002:2D7 003:2E7 004:27B 005:2BB 006:2DB 007:2EB 008:27D 009:2BD 00A:2DD 00B:2ED 00C:27E 00D:2BE 00E:2DE 00F:2EE 010:177 011:1B7 012:1D7 013:1E7 014:17B 015:1BB 016:1DB 017:1EB 018:17D 019:1BD 01A:1DD 01B:1ED 01C:17E 01D:1BE 01E:1DE 01F:1EE Subgroup gd4: (mapping of 4-bit data word into 10-bit code word) 000:15F 001:16F 002:19F 003:1AF 004:25F 005:26F 006:29F 007:2AF 008:1F5 009:1F6 00A:1F9 00B:1FA 00C:2F5 00D:2F6 00E:2F9 00F:2FA Subgroup gd3: (mapping of 3-bit data word into 10-bit code word) 000:13F 001:1CF 002:23F 003:2CF 004:1F3 005:1FC 006:2F3 007:2FC Subgroup ge5: (mapping of 5-bit data word into 10-bit code word) 000:377 001:37B 002:37D 003:37E 004:3B7 005:3BB 006:3BD 007:3BE 008:3D7 009:3DB 00A:3DD 00B:3DE 00C:3E7 00D:3EB 00E:3ED 00F:3EE 010:17F 011:1BF 012:1DF 013:1EF 014:27F 015:2BF 016:2DF 017:2EF 018:1F7 019:1FB 01A:1FD 01B:1FE 01C:2F7 01D:2FB 01E:2FD 01F:2FE Subgroup ge3: (mapping of 3-bit data word into 10-bit code word) 000:35F 001:36F 002:39F 003:3AF 004:3F5 005:3F6 006:3F9 007:3FA Subgroup gf3: (mapping of 3-bit data word into 10-bit code word) 000:37F 001:3BF 002:3DF 003:3EF 004:3F7 005:3FB 006:3FD 007:3FE

The third fragment is then mapped into an ‘h’ group word to maintain the running digital sum within +/−4. This mapping takes into account the current running digital sum of the system and the running digital sum of the ‘g’ group segment. The selection of the ‘h’ group code can be separated into three cases, depending on the current running digital sum of the system. The first case is if the current RDS is −4, the second case is if the RDS is −2 and the third case is if the RDS is 0. The cases of RDS being +4 or +2 are just the inverse of −4 and −2. Although there are different ways to group the ‘h’ groups, table 3 shows groupings according to various running digital sums. The ‘h’ groups can be chosen that correspond to collections from the ‘g’ subgroups. In some instances, the inverse, or −gxx, of the subgroup is chosen. Also, there are situations where the ‘h’ group word is larger (has more bits) than the corresponding mapping ‘g’ group (i.e. a fragment from the group ha8 is mapped to the group gc6). Here, the least significant bits of the third fragment are chosen to map the ‘h’ group according to the corresponding ‘g’ group. TABLE 3 Mapping Table of user fragments into ‘h’ group words. Subgroup ha8 includes 256 patterns and they are from gc7, gc6 and gd6. Since 2⁸ = 256, these code words are exactly enough for the encoding of 8-bit data words. Mappings of 8-bit data word to these 10-bit code words of subgroup ha8 are: Data 000 to 07F : gc7(128 patterns, RDS=+2) Data 080 to 0BF : gc6(64 patterns, RDS=+2) Data 0C0 to 0FF : gd6(64 patterns, RDS=+4) Subgroup ha6 includes 64 patterns and they are from gd5 and ge5. Mappings of 6-bit data word to these 10-bit code words are: Data 000 to 01F : gd5(32 patterns, RDS=+4) Data 020 to 03F : ge5(32 patterns, RDS=+6) Subgroup ha5 includes 32 patterns and they are from gc4 and gd4. Mappings of 5-bit data word to these 10-bit code words are: Data 000 to 00F : gc4(16 patterns, RDS=+2) Data 010 to 01F : gd4(16 patterns, RDS=+4) Subgroup ha4 includes 16 patterns and they are from gd3 and ge3. Mappings of 4-bit data word to these 10-bit code words are: Data 000 to 007 : gd3(8 patterns, RDS=+4) Data 008 to 00F : ge3(8 patterns, RDS=+6) Note that all “ha” patterns have RDS of +2, +4 or +6. Subgroup hb9 includes 512 patterns and they are from ha8, gb7, gb6, gb5, gb4, gb3 and gf3. Mappings of 9-bit data word to these 10-bit code words are: Data 000 to 0FF : ha8(256 patterns, RDS=+2, +4) Data 100 to 17F : gb7(128 patterns, RDS= 0) Data 180 to 1BF : gb6(64 patterns, RDS= 0) Data 1C0 to 1DF : gb5(32 patterns, RDS= 0) Data 1E0 to 1EF : gb4(16 patterns, RDS= 0) Data 1F0 to 1F7 : 9b3(8 patterns, RDS= 0) Data 1F8 to 1FF : gf3(8 patterns, RDS=+8) Subgroup hb6 includes 64 patterns and they are the same as ha6. Mappings of 6-bit data word to these 10-bit code words are: Data 000 to 03F : ha6(64 patterns, RDS=+4, +6) Subgroup hb5 includes 32 patterns and they are the same as ha5. Mappings of 5-bit data word to these 10-bit code words are: Data 000 to 01F : ha5(32 patterns, RDS=+2, +4) Subgroup hb4 includes 16 patterns and they are the same as ha4. Mappings of 4-bit data word to these 10-bit code words are: Data 000 to 00F : ha4(16 patterns, RDS=+4, +6) All “hb” patterns have RDS of 0, +2, +4, +6 or +8. Subgroup hc9 includes 512 patterns and they are from ha8, gb7, gb6, gb5, gb4, gb3 gb2, gc1 and- gc1. Mappings of 9-bit data word to these 10-bit code words are: Data 000 to 0FF : ha8(256 patterns, RDS= +2, +4) Data 100 to 17F : gb7(128 patterns, RDS= 0) Data 180 to 1BF : gb6(64 patterns, RDS= 0) Data 1C0 to 1DF : gb5(32 patterns, RDS= 0) Data 1E0 to 1EF : gb4(16 patterns, RDS= 0) Data 1F0 to 1F7 : gb3(8 patterns, RDS= 0) Data 1F8 to 1FB : gb2(4 patterns, RDS= 0) Data 1FC to 1FD : gc1(2 patterns, RDS= +2) Data 1FE to 1FF : −gc1(2 patterns, RDS= −2) Subgroup hc8 includes 256 patterns and they are from −gc7, −gc6 and ha6. Mappings of 8-bit data word to these 10-bit code words are: Data 000 to 07F : −gc7(128 patterns, RDS= −2) Data 080 to 0BF : −gc6(64 patterns, RDS= −2) Data 0C0 to 0FF : ha6(64 patterns, RDS= +4, +6) Subgroup hc6 includes 64 patterns and they are from ha5, −gc4 and ha4. Mappings of 6-bit data word to these 10-bit code words are: Data 000 to 01E : ha5(32 patterns, RDS= +2, +4) Data 020 to 02F : −gc4(16 patterns, RDS= −2) Data 030 to 03F : ha4(16 patterns, RDS= +4, +6) All “hc” patterns have RDS of−2, 0, +2, +4, or +6. Subgroup hd9 includes 512 patterns and they are the same as hc9. Mappings of 9-bit data word to these 10-bit code words are: Data 000 to 1FF : hc9(512 patterns, RDS= −2, 0, +2, +4) Subgroup hd8 includes 256 patterns and they are from −gc7, −gc6, gd5 and −gd5. Mappings of 8-bit data word to these 10-bit code words are: Data 000 to 07F : −gc7(128 patterns, RDS= −2) Data 080 to 0BF : −gc6(64 patterns, RDS= −2) Data 0C0 to 0DF : gd5(32 patterns, RDS= +4) Data 0E0 to 0FF : −gd5(32 patterns, RDS= −4) Subgroup hd7 includes 128 patterns and they are from −gd6, ha5, −gc4, gd3, and −gd3. Mappings of 8-bit data word to these 10-bit code words are: Data 000 to 03F : −gd6(64 patterns, RDS= −4) Data 040 to 05F : ha5(32 patterns, RDS= +2, +4) Data 060 to 06F : −gc4(16 patterns, RDS= −2) Data 070 to 077 : gd3(8 patterns, RDS= +4) Data 078 to 07F : −gd3(8 patterns, RDS= −4) All “hd” patterns have RDS of −4, −2, 0, +2 or +4. Subgroup he9 includes 512 patterns and they are the equivalent to the inverse of hc9. Mappings of 9-bit data word to these 10-bit code words are: Data 000 to 1FF : −hc9(512 patterns, RDS= −4, −2, 0, +2) Subgroup he8 includes 256 patterns and they are the equivalent to the inverse of hc8. Mappings of 8-bit data word to these 10-bit code words are: Data 000 to 0FF : −hc8(256 patterns, RDS= −6, −4, +2) All “he” patterns have RDS of −6, −4, −2, 0, or +2.

The lookup tables can be assembled based on the current state and the ‘g’ group and ‘h’ group words. Tables 4 to 6 indicate how the 19-bit data words can be mapped into 20-bit code words. The 19-bit data word is broken into three fragments. The first fragment is a bit pattern of the most significant bits of the data word. The second and third fragments are mapped into ‘g’ and ‘h’ segments, respectively. The 20-bit code word is composed of two 10-bit code segments. The first code segment is selected from the ‘g’ group and the second code segment is selected from the ‘h’ group. Depending on the current state of the encoder, code words are chosen from the corresponding table. Tables for states −4,−2 and 0 are shown while state +4 uses the inverse code words for state −4 and state +2 uses the inverse code words for state −2. In the lookup tables, “Pn.” stands for the particular pattern number of the mapping performed. There are 39 patterns for state −4, 19 patterns for state −2 and 16 patterns for state 0. The values “G type” and “H type” correspond to which ‘g’ and ‘h’ subgroup is in the particular pattern. These values can further be used when decoding the code word. TABLE 4 Lookup table for data word when current state is −4. Starting State = S (−4) 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Pn. G type H type 0 0 0 gb7 hb9 1 07 19 0 0 1 gc7 hc9 2 17 29 0 1 0 0 −gc7 ha8 3 97 08 0 1 0 1 gb6 hb9 4 06 19 0 1 1 0 gc7 hc8 5 17 28 0 1 1 1 gc6 hc9 6 16 29 1 0 0 0 gd6 hd9 7 26 39 1 0 0 1 0 −gc6 ha8 8 96 08 1 0 0 1 1 gb5 hb9 9 05 19 1 0 1 0 0 gc6 hc8 10 16 28 1 0 1 0 1 gd6 hd8 11 26 38 1 0 1 1 0 gd5 hd9 12 25 39 1 0 1 1 1 ge5 he9 13 35 49 1 1 0 0 0 0 −gc7 ha6 14 97 06 1 1 0 0 0 1 gb7 hb6 15 07 16 1 1 0 0 1 0 gb4 hb9 16 04 19 1 1 0 0 1 1 gc7 hc6 17 17 26 1 1 0 1 0 0 gc4 hc9 18 14 29 1 1 0 1 0 1 gd6 hd7 19 26 37 1 1 0 1 1 0 gd5 hd8 20 25 38 1 1 0 1 1 1 gd4 hd9 21 24 39 1 1 1 0 0 0 ge5 he8 22 35 48 1 1 1 0 0 1 0 −gc7 ha5 23 97 05 1 1 1 0 0 1 1 −gc6 ha6 24 96 06 1 1 1 0 1 0 0 gb7 hb5 25 07 15 1 1 1 0 1 0 1 gb6 hb6 26 06 16 1 1 1 0 1 1 0 gb3 hb9 27 03 19 1 1 1 0 1 1 1 gc6 hc6 28 16 26 1 1 1 1 0 0 0 gc4 hc8 29 14 28 1 1 1 1 0 0 1 gd5 hd7 30 25 37 1 1 1 1 0 1 0 gd4 hd8 31 24 38 1 1 1 1 0 1 1 gd3 hd9 32 23 39 1 1 1 1 1 0 0 ge3 he9 33 33 49 1 1 1 1 1 0 1 0 −gc7 ha4 34 97 04 1 1 1 1 1 0 1 1 −gc6 ha5 35 96 05 1 1 1 1 1 1 0 0 gb7 hb4 36 07 14 1 1 1 1 1 1 0 1 gb6 hb5 37 06 15 1 1 1 1 1 1 1 0 gb5 hb6 38 05 16 1 1 1 1 1 1 1 1 gd4 hd7 39 24 37

TABLE 5 Lookup table for data word when current state is −2. Starting State = S (−2) 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Pn. G type H type 0 0 0 −gc7 hb9 1 97 19 0 0 1 gb7 hc9 2 07 29 0 1 0 gc7 hd9 3 17 39 0 1 1 0 −gc6 hb9 4 96 19 0 1 1 1 gb7 hc8 5 07 28 1 0 0 0 gb6 hc9 6 06 29 1 0 0 1 gc7 hd8 7 17 38 1 0 1 0 gc6 hd9 8 16 39 1 0 1 1 gd6 he9 9 26 49 1 1 0 0 0 gb6 hc8 10 06 28 1 1 0 0 1 gb5 hc9 11 05 29 1 1 0 1 0 gc7 hd7 12 17 37 1 1 0 1 1 gc6 hd8 13 16 38 1 1 1 0 0 gd6 he8 14 26 48 1 1 1 0 1 ge5 −hb9 15 35 59 1 1 1 1 0 0 −gc7 hb6 16 97 16 1 1 1 1 0 1 gb7 hc6 17 07 26 1 1 1 1 1 0 gb5 hc8 18 05 28 1 1 1 1 1 1 gb4 hc9 19 04 29

TABLE 6 Lookup table for data word when current state is 0. Starting State = S0 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Pn. G type H type 0 0 0 −gc7 hc9 1 97 29 0 0 1 gb7 hd9 2 07 39 0 1 0 gc7 he9 3 17 49 0 1 1 0 −gc7 hc8 4 97 28 0 1 1 1 −gc6 hc9 5 96 29 1 0 0 0 gb7 hd8 6 07 38 1 0 0 1 gb6 hd9 7 06 39 1 0 1 0 gc7 he8 8 17 48 1 0 1 1 gc6 he9 9 16 49 1 1 0 0 gd6 −hb9 10 26 59 1 1 0 1 0 −gc6 hc8 11 96 28 1 1 0 1 1 gb7 hd7 12 07 37 1 1 1 0 0 gb6 hd8 13 06 38 1 1 1 0 1 gb5 hd9 14 05 39 1 1 1 1 0 gc6 he8 15 16 48 1 1 1 1 1 gd5 −hb9 16 25 59

As an example, assume the 19-bit user data received in step 202 is 0×2A3EC =010 1010 0011 1110 1100 and the current state received in step 204 is −4. Assuming the leading bit is d18, d18=0, d17=1, d16=0, d15=1, d14=0, d13=1, d12=0, d11=0, d10=0, d9=1, d8=1, d7=1, d6=1, d5=1, d4=0, d3=1, d2=1, d1=0, d0=0. According to Table 4, which is for state −4, when d(18:15)=0101, which is the first fragment, d(14:9) (the second fragment) is mapped according to subgroup “gb6” to obtain the first 10-bit segment and d(8:0) (the third fragment) is mapped according to subgroup “hb9” to obtain the second 10-bit segment of the 20-bit code word. As ascertained from the data word, the second fragment d(14:9) is 010001=0×011. In step 210, according to the mapping table for subgroup “gb6”, the 10-bit segment should be 0×343=1101000011. For the second 10-bit segment of the code word, as obtained in step 212, the third fragment d(8:0)=111101100=0×1EC is mapped according to the mapping table for subgroup “hb9”. Data between 0×1E=111100000 and 0×1EF=111101111 should use patterns from “gb4”. Here, the four least significant bits d(3:0)=1100=0×00C are mapped according to the mapping table for subgroup “gb4”. As a result, 0×00C maps into 0×08F=0010001111. Now, combining the first and second 10-bit segments in step 214 is performed to obtain the 20-bit code word of 1101000011 0010001111=0×D0C8F. The running digital sum of this code word is 0, thus the current state will remain −4 (−4+0=−4).

In one embodiment, the unrestrained sequence of 101010 . . . is avoided. Code words having this sequence are eliminated. As a result, code words 0×AAAAA and 0×55555 are replaced by other code words, for example 0×83EAA and 0×43D55, respectively. These two examples are not used for other mappings and have the same RDS as the replaced patterns.

The details of the circuits and operations described below are examples and can be performed in hardware, software, firmware and/or combinations thereof. The functions of the circuits can be described with respect to various logic operations. In the case of circuits, these may be formed on one chip or various chips, as desired. Table 7 provides definitions for the symbols and logic operations used. TABLE 7 Symbol definition: “|” Bitwise OR “&” Bitwise AND “{circumflex over ( )}” Bitwise XOR “!x” Inverse of bit x “!C(n:0)” Inverse of all bits of word C

FIG. 3 illustrates a block diagram of an encoder 250 for encoding a user data word of 19 bits to a 20-bit code word. Encoder 250 communicates to a communications channel 252, which can comprise an arrangement of magnetic storage discs and heads as shown in FIG. 1. Channel 252 can also be other types of communication channels such as an optical, wireless or transmission line channel.

Encoder 250 receives as input an initialization signal, a user data word I_(18:0) and a word clock. Encoder 250 outputs a code word W_(19:0) to communication channel 252. An encoder input circuit 254 receives input to the encoder 250 as well as the next state of the system. The encoder input circuit 254 outputs a data word D_(18:0) and a pattern select value tt_(11:0) to encoder circuits 256, 258 and 260, identified as enc_r4, enc_r2 and enc_r0. Encoder circuit 254 also provides a state value to a GX encoder 262, an HX encoder 264 and an encoder output circuit 266. The GX encoder 262 and HX encoder 264 receive values from encoder circuits 256, 258 and 260 in order to generate the ‘g’ group words and the ‘h’ group words. The GX encoder 262 and HX encoder 264 provide the ‘g’ group words and ‘h’ group words to the encoder output circuit 266. Ultimately, output encoder circuit 266 provides a code word to communication channel 252.

FIG. 4 illustrates a block diagram of encoder input circuit 254. Encoder input 254 includes a state register 270, a 19-bit data word block 272 and a pattern select circuit 274. Before the first data word is clocked into the input block, the initialization signal (Init) is used to initialize the state to zero. State is a four-bit sign value representing the current state. The next state value is received from the encoder output circuit 266 and is clocked in as the current state upon the rising edge of the word clock. Additionally, at 19-bit data word block 272, the data word I_(18:0) is clocked in upon a rising edge of the word clock. The 19-bit data word is sent to pattern select circuit 274. Pattern select circuit 274 prepares a value tt_(11:0) indicative of the four most significant bits of the data word. Encoder input circuit 254 operates in a manner shown in Table 8. TABLE 8 Input: I_(18:0) (19 bits), Init, Word Clock, Next State_(3:0) Output: D_(18:0) , tt_(11:0), State_(3:0) Pattern Select  tt0 =!d18& d17&!d16&!d15 tt1 =!d18& d17&!d16& d15  tt2 =!d18& d17& d16&!d15 tt3 =!d18& d17& d16& d15  tt4 = d18&!d17&!d16&!d15 tt5 = d18&!d17&!d16& d15  tt6 = d18&!d17& d16&!d15 tt7 = d18&!d17& d16& d15  tt8 = d18& d17&!d16&!d15 tt9 = d18& d17&!d16& d15  tt10= d18& d17& d16&!d15 tt11= d18& d17& d16& d15

FIG. 5 illustrates a block diagram of encoder circuit 256, identified as enc_r4. Encoder circuit 256 includes a pattern select circuit 280 and a mux circuit 282. Encoder circuit 256 operates to select a code word when the current state is 4. Pattern select circuit 280 selects which of the 39 patterns of the lookup table shown in Table 4 is used given the data word d_(18:0). The value that pattern select circuit 280 issues is a 39-bit word indicating which pattern should be selected. Mux circuit 282 utilizes the select value S_(39:1) and the data word D_(18:0) to output a selection of which ‘g’ subgroup to use (g4S_(15:0)), which bits of the data word will be mapped to the ‘g’ word (g4w_(6:0)), which ‘h’ subgroup to use (h4s_(15:0)) and which bits of data word will be used to map the ‘h’ word (h4w_(8:0)). The calculations of encoder circuit 256 are shown in Table 9. TABLE 9 Input: d18,d17,d16,d15,d14,d13,d12,d11,d10,d9,d8,d7,d6,d5,d4,d3,d2,d1,d0 (19-bit Dataword) tt11,tt10,tt9,tt8,tt7,tt6,tt5,tt4,tt3,tt2,tt1,tt0 Output: g4w6,g4w5,g4w4,g4w3,g4w2,g4w1,g4w0      (7-bit word) g4s15,g4s14,g4s13,g4s12,g4s11,g4s10,g4s9,g4s8,g4s7,g4s6,g4s5,g4s4,g4s3,g4s2,g4s1,g4s0 h4w8,h4w7,h4w6,h4w5,h4w4,h4w3,h4w2,h4w1,h4w0 (9-bit word) h4s15,h4s14,h4s13,h4s12,h4s11,h4s10,h4s9,h4s8,h4s7,h4s6,h4s5,h4s4,h4s3,h4s2,h4s1,h4s0 Pattern Select of enc_r4 t4 = tt0 t5 = tt1 t6 = tt2 t7 = tt3 t8 = tt4 t9 = tt5 ta = tt6 tb = tt7 tc = tt8 td = tt9 te = tt10 tf = tt11 S1 =!d18&!d17&!d16 S2 =!d18&!d17& d16 S3 =t4 S4 =t5 S5 =t6 S6 =t7 S7 =t8 S8 =t9&!d14 S9 =t9& d14 S10=ta&!d14 S11=ta& d14 S12=tb&!d14 S13=tb& d14 S14=tc&!d14&!d13 S15=tc&!d14& d13 S16=tc& d14&!d13 S17=tc& d14& d13 S18=td&!d14&!d13 S19=td&!d14& d13 S20=td& d14&!d13 S21=td& d14& d13 S22=te&!d14&!d13 S23=te&!d14& d13&!d12 S24=te&!d14& d13& d12 S25=te& d14&!d13&!d12 S26=te& d14&!d13& d12 S27=te& d14& d13&!d12 S28=te& d14& d13& d12 S29=tf&!d14&!d13&!d12 S30=tf&!d14&!d13& d12 S31=tf&!d14& d13&!d12 S32=tf&!d14& d13& d12 S33=tf& d14&!d13&!d12 S34=tf& d14&!d13& d12&!d11 S35=tf& d14&!d13& d12&d11 S36=tf& d14& d13&!d12&!d11 S37=tf& d14& d13&!d12&d11 S38=tf& d14& d13& d12&!d11 S39=tf& d14& d13& d12&d11 MUX for GX and HX Encoder of enc_r4 For GX: if(S1|S2|S4|S6|S7|S9|S12|S13|S16|S18|S21|S27|S32|S33) {g4w(6:0) = (d15,d14,d13,d12,d11,d10,d9) } if(S3|S5|S8|S10|S11|S20|S22|S29|S31) {g4w(6:0) = (d14,d13,d12,d11,d10, d9,d8) } if(S19|S30|S39) {g4w(6:0) = (d13,d12,d11,d10, d9, d8,d7) } if(S14|S15|S17|S24|S26|S28|S38) {g4w(6:0) = (d12,d11,d10, d9, d8, d7,d6) } if(S23|S25|S35|S37) {g4w(6:0) = (d11,d10, d9, d8, d7, d6,d5) } if(S34|S36) {g4w(6:0) = (d10, d9, d8, d7, d6, d5,d4) } if(S3|S14|S23|S34) {g4s0=1,  all other g4s=0 } if(S8|S24|S35) {g4s1=1,  all other g4s=0 } if(S1|S15|S25|S36) {g4s2=1,  all other g4s=0 } if(S4|S26|S37) {g4s3=1,  all other g4s=0 } if(S9|S38) {g4s4=1,  all other g4s=0 } if(S16) {g4s5=1,  all other g4s=0 } if(S27) {g4s6=1,  all other g4s=0 } if(S2|S5|S17) {g4s7=1,  all other g4s=0 } if(S6|S10|S28) {g4s8=1,  all other g4s=0 } if(S18|S29) {g4s9=1,  all other g4s=0 } if(S7|S11|S19) {g4s10=1, all other g4s=0 } if(S12|S20|S30) {g4s11=1, all other g4s=0 } if(S21|S31|S39) {g4s12=1, all other g4s=0 } if(S32) {g4s13=1, all other g4s=0 } if(S13|S22) {g4s14=1, all other g4s=0 } if(S33) {g4s15=1, all other g4s=0 } For HX: h4w(8:0) = (d8,d7,d6,d5,d4,d3,d2,d1,d0) if(S3|S8) {h4s0=1,  all other h4s=0 } if(S14|S24) {h4s1=1,  all other h4s=0 } if(S23|S35) {h4s2=1,  all other h4s=0 } if(S34) {h4s3=1,  all other h4s=0 } if(S1|S4|S9|S16|S27) {h4s4=1,  all other h4s=0 } if(S15|S26|S38) {h4s5=1,  all other h4s=0 } if(S25|S37) {h4s6=1,  all other h4s=0 } if(S36) {h4s7=1,  all other h4s=0 } if(S2|S6|S18) {h4s8=1,  all other h4s=0 } if(S5|S10|S29) {h4s9=1,  all other h4s=0 } if(S17|S28) {h4s10=1, all other h4s=0 } if(S7|S12|S21|S32) {h4s11=1, all other h4s=0 } if(S11|S20|S31) {h4s12=1, all other h4s=0 } if(S19|S30|S39) {h4s13=1, all other h4s=0 } if(S13|S33) {h4s14=1, all other h4s=0 } if(S22) {h4s15=1, all other h4s=0 }

Encoder circuits 258 and 260, shown in block diagrams in FIGS. 6 and 7, operate similar to encoder circuit 256. Encoder circuit 258 includes a pattern select circuit 290 that selects a particular pattern from the lookup table in Table 5 and mux circuit 292 indicates the appropriate ‘g’ and ‘h’ subgroups and the bits of the data word that will be used for the ‘g’ and ‘h’ mappings. Encoder circuit 260 includes pattern select circuit 300 and mux circuit 302. Pattern select circuit 300 indicates which pattern should be used when the current state is zero. Mux circuit 302 outputs the appropriate ‘g’ and ‘h’ subgroups and the bits used for the respective ‘g’ and ‘h’ mappings. Encoder circuits 258 and 260 operate according to the tables shown in tables 10 and 11, respectively. TABLE 10 Input: d18,d17,d16,d15,d14,d13,d12,d11,d10,d9,d8,d7,d6,d5,d4,d3,d2,d1,d0 (19-bit Dataword) tt11,tt10,tt9,tt8,tt7,tt6,tt5,tt4,tt3,tt2,tt1,tt0 Output: g2w6,g2w5,g2w4,g2w3,g2w2,g2w1,g2w0      (7-bit word) g2s9,g2s8,g2s7,g2s6,g2s5,g2s4,g2s3,g2s2,g2s1,g2s0 h2w8,h2w7,h2w6,h2w5,h2w4,h2w3,h2w2,h2w1,h2w0 (9-bit word) h2s10,h2s9,h2s8,h2s7,h2s6,h2s5,h2s4,h2s3,h2s2,h2s1,h2s0 Pattern Select of enc_r2 t6 = tt2 t7 = tt3 t8 = tt4 t9 = tt5 ta = tt6 tb = tt7 tc = tt8 td = tt9 te = tt10 tf = tt11 S1 =!d18&!d17&!d16 S2 =!d18&!d17& d16 S3 =!d18& d17&!d16 S4 =t6 S5 =t7 S6 =t8 S7 =t9 S8 =ta S9 =tb S10 =tc&!d14 S11=tc& d14 S12=td&!d14 S13=td& d14 S14=te&!d14 S15=te& d14 S16=tf&!d14&!d13 S17=tf&!d14& d13 S18=tf& d14&!d13 S19=tf& d14& d13 MUX for GX and HX Encoder of enc_r2 For GX: if(S1|S2|S3|S4|S6|S8|S9|S11|S15|S19) {g2w(6:0) = (d15,d14,d13,d12,d11,d10,d9) } if(S5|S7|S10|S13|S14|S18) {g2w(6:0) = (d14,d13,d12,d11,d10, d9,d8) } if(S12) {g2w(6:0) = (d13,d12,d11,d10, d9, d8,d7) } if(S16|S17) {g2w(6:0) = (d12,d11,d10, d9, d8, d7,d6) } if(S1|S16) {g2s0=1,  all other g2s=0 } if(S4) {g2s1=1,  all other g2s=0 } if(S2|S5|S17) {g2s2=1,  all other g2s=0 } if(S6|S10) {g2s3=1,  all other g2s=0 } if(S11|S18) {g2s4=1,  all other g2s=0 } if(S19) {g2s5=1,  all other g2s=0 } if(S3|S7|S12) {g2s6=1,  all other g2s=0 } if(S8|S13) {g2s7=1,  all other g2s=0 } if(S9|S14) {g2s8=1,  all other g2s=0 } if(S15) {g2s9=1,  all other g2s=0 } For HX: h2w(8:0) = (d8,d7,d6,d5,d4,d3,d2,d1,d0) if(S1|S4) {h2s0=1,  all other h2s=0 } if(S16) {h2s1=1,  all other h2s=0 } if(S2|S6|S11|S19) {h2s2=1,  all other h2s=0 } if(S5|S10|S18) {h2s3=1,  all other h2s=0 } if(S17) {h2s4=1,  all other h2s=0 } if(S3|S8) {h2s5=1,  all other h2s=0 } if(S7|S13) {h2s6=1,  all other h2s=0 } if(S12) {h2s7=1,  all other h2s=0 } if(S9) {h2s8=1,  all other h2s=0 } if(S14) {h2s9=1,  all other h2s=0 } if(S15) {h2s10=1, all other h2s=0 }

TABLE 11 enc_r0 Input: d18,d17,d16,d15,d14,d13,d12,d11,d10,d9,d8,d7,d6,d5,d4,d3,d2,d1,d0 (19-bit Dataword) tt11,tt10,tt9,tt8,tt7,tt6,tt5,tt4,tt3,tt2,tt1,tt0 Output: g0w6,g0w5,g0w4,g0w3,g0w2,g0w1,g0w0      (7-bit word) g0s8,g0s7,g0s6,g0s5,g0s4,g0s3,g0s2,g0s1,g0s0 h0w8,h0w7,h0w6,h0w5,h0w4,h0w3,h0w2,h0w1,h0w0 (9-bit word) h0s7,h0s6,h0s5,h0s4,h0s3,h0s2,h0s1,h0s0 Pattern Select of enc_r0 t6 = tt2 t7 = tt3 t8 = tt4 t9 = tt5 ta = tt6 tb = tt7 tc = tt8 td = tt9 te = tt10 tf = tt11 S1 =!d18&!d17&!d16 S2 =!d18&!d17& d16 S3 =!d18& d17&!d16 S4 =t6 S5 =t7 S6 =t8 S7 =t9 S8 =ta S9 =tb S10=tc S11=td&!d14 S12=td& d14 S13=te&!d14 S14=te& d14 S15=tf&!d14 S16=tf& d14 MUX for GX and HX Encoder of enc_r0 For GX: if(S1|S2|S3|S5|S7|S9|S10|S14|S16) {g0w(6:0) = (d15,d14,d13,d12,d11,d10,d9) } if(S4|S6|S8|S11|S13|S15) {g0w(6:0) = (d14,d13,d12,d11,d10, d9,d8) } if(S12) {g0w(6:0) = (d13,d12,d11,d10, d9, d8,d7) } if(S1|S4) {g0s0=1,  all other g0s=0 } if(S5|S11) {g0s1=1,  all other g0s=0 } if(S2|S6|S12) {g0s2=1,  all other g0s=0 } if(S7|S13) {g0s3=1,  all other g0s=0 } if(S14) {g0s4=1,  all other g0s=0 } if(S3|S8) {g0s5=1,  all other g0s=0 } if(S9|S15) {g0s6=1,  all other g0s=0 } if(S10) {g0s7=1,  all other g0s=0 } if(S16) {g0s8=1,  all other g0s=0 } For HX: h0w(8:0) = (d8,d7,d6,d5,d4,d3,d2,d1,d0) if(S1|S5) {h0s0=1,  all other h0s=0 } if(S4|S11) {h0s1=1,  all other h0s=0 } if(S2|S7|S14) {h0s2=1,  all other h0s=0 } if(S6|S13) {h0s3=1,  all other h0s=0 } if(S12) {h0s4=1,  all other h0s=0 } if(S3|S9) {h0s5=1,  all other h0s=0 } if(S8|S15) {h0s6=1,  all other h0s=0 } if(S10|S16) {h0s7=1,  all other h0s=0 }

FIG. 8 illustrates a block diagram of GX encoder 262. GX encoder 262 includes an GX encoder input mux 310, a plurality of subgroup encoder circuits 312 and a GX encoder output mux 314. GX encoder input mux 310 receives the ‘g’ values from the encoder circuits 256, 258 and 260 (g4w, g2w, g0w, g4w_sel, g2w_(— sel, g)0w_sel). Input mux 310 also receives the current state from encoder input circuit 254. Encoder input mux 310 sends the appropriate ‘g’ bits (the second fragment) received through each of the plurality of subgroup encoder circuits 312 based on the ‘g’ select values and the current state. The plurality of encoder circuits 312 map the second fragment (gw_in_(6:0)) according to the mapping table of Table 2. The mapped 10-bit segments are then output to the GX encoder output mux 314. In the event an inverse of the mapped subgroups is necessary, for example from enc_gx7 and enc_gc6, inverter circuits 316 are provided to invert the output from these respective circuits and send it to the GX encoder output mux 314. The GX encoder output mux selects the appropriate 10-bit segment according to the ‘g’ select value sent from GX encoder input mux 310. The GX encoder 262 operates according to calculations shown in Table 12.

FIG. 9 illustrates a block diagram of HX encoder 264, which operates similar to GX encoder 262. HX encoder 264 includes an HX encoder input mux 320, a plurality of subgroup encoder circuits 322 and an HX encoder output mux 324. HX encoder input mux 320 receives a signal indicative of the current state from the encoder input circuit 254 and ‘h’ values (h4w, h2w, h0w, h4s, h2s, h0s) from encoder circuits 256, 258 and 260. HX encoder input mux 320 selects the appropriate third fragment (either h4w, h2w and h0w) based on the current state and select values (h4s, h2s, h0s) and outputs the selection as hw_in. Also, HX encoder input mux 320 selects the particular subgroup based on the state and outputs a value h_sel based on the state. The plurality of subgroup encoder circuits 322 map the second fragment and send their respective mapped segments to the HX encoder output mux 324. The HX encoder output mux 324 selects the appropriate 10-bit segment based on h_sel. The 10-bit segment is then sent to encoder output circuit 266. The HX encoder 264 operates according to calculations shown in Table 13. TABLE 13 HX Encoder Input: h4w(6:0), h2w(6:0), h0w(6:0), h4s(15:0), h2s(10:0), h0s(7:0), State(3:0) Output: hw(9:0) HX Encoder Input Mux Input: h4w(8:0), h2w(8:0), h0w(8:0), h4s(15:0), h2s(10:0), h0s(7:0), State(3:0) Output: hw_in(8:0), h_sel(16:0) State(3:0) is a 4-bit signed value representing the current state. if (State= −4 or State= 4)  { hw_in(8:0) = h4w(8:0), h_sel(15:0) = h4s(15:0),  h_sel(16) =0 } if (State= −2 or State= 2)  { hw_in(8:0) = h2w(8:0), h_sel(0) =0, h_sel(1) =0, h_sel(2) =0, h_sel(3) =0, h_sel(4) =h2s(0), h_sel(5) =h2s(1), h_sel(6) =0, h_sel(7) =0, h_sel(8) =h2s(2), h_sel(9) =h2s(3), h_sel(10)=h2s(4), h_sel(11)=h2s(5), h_sel(12)=h2s(6), h_sel(13)=h2s(7), h_sel(14)=h2s(8), h_sel(15)=h2s(9), h_sel(16)=h2s(10), } if (State= 0)  { hw_in(8:0) = h0w(8:0), h_sel(0) =0, h_sel(1) =0, h_sel(2) =0, h_sel(3) =0, h_sel(4) =0, h_sel(5) =0, h_sel(6) =0, h_sel(7) =0, h_sel(8) =h0s(0), h_sel(9) =h0s(1), h_sel(10)=0, h_sel(11)=h0s(2), h_sel(12)=h0s(3), h_sel(13)=h0s(4), h_sel(14)=h0s(5), h_sel(15)=h0s(6), h_sel(16)=h0s(7), } Note: All the encoders enc_gc7, enc_gc6, enc_gc5, enc_gc4, enc_gc3, enc_gd6, enc_gd5, enc_gd4, enc_gd3, enc_ge5 and enc_ge3 used here in HX Encoder are identical to those defined in the GX Encoder. enc_ha8 Input: A(7:0) Output: CW(9:0) if(!A7) CW(9:0) = enc_gc7(A(6:0)); if(A7&!A6) CW(9:0) = enc_gc6(A(5:0)); if(A7&A6) CW(9:0)= enc_gd6(A(5:0)); Note: CW(9:0)= enc_gc7(A(6:0)); means CW(9:0) is equal to the 10-bit output of block enc_gc7 when A(6:0) is the input to it. enc_ha6 Input: A(5:0) Output: CW(9:0) if(!A5) CW(9:0)= enc_gd5(A(4:0)); if(A5) CW(9:0)= enc_ge5(A(4:0)); enc_ha5 Input: A(4:0) Output: CW(9:0) if(!A4) CW(9:0)= enc_gc4(A(3:0)); if(A4) CW(9:0)= enc_gd4(A(3:0)); enc_ha4 Input: A(3:0) Output: CW(9:0) if(!A3) CW(9:0)= enc_gd3(A(2:0)); if(A3) CW(9:0)= enc_ge3(A(2:0)); enc_hb9 Input: A(8:0) Output: CW(9:0) if(!A8) CW(9:0)= enc_ha8(A(7:0)); if(A8&!A7) CW(9:0)= enc_gb7(A(6:0)); if(A8&A7&!A6) CW(9:0)= enc_gb6(A(5:0)); if(A8&A7&A6&!A5) CW(9:0)= enc_gb5(A(4:0)); if(A8&A7&A6&A5&!A4) CW(9:0)= enc_gb4(A(3:0)); if(A8&A7&A6&A5&A4&!A3) CW(9:0)= enc_gb3(A(2:0)); if(A8&A7&A6&A5&A4& A3) CW(9:0)= enc_gf3(A(2:0)); enc_gf3 Input: A42,A1,A0 Output: C9,C8,C7,C6,C5,C4,C3,C2,C1,C0 gf3a = !A2; gf3a9= gf3a; gf3a8= gf3a; gf3a7= gf3a &(  A1 |  A0 ); gf3a6= gf3a &(  A1 | !A0 ); gf3a5= gf3a &(  A0 | !A1 ); gf3a4= gf3a &( !A1 | !A0 ); gf3a3= gf3a; gf3a2= gf3a; gf3a1= gf3a; gf3a0= gf3a; gf3b = A2; gf3b9= gf3b; gf3b8= gf3b; gf3b7= gf3b; gf3b6= gf3b; gf3b5= gf3b; gf3b4= gf3b; gf3b3= gf3b &(  A1 |  A0 ); gf3b2= gf3b &(  A1 | !A0 ); gf3b1= gf3b &(  A0 | !A1 ); gf3b0= gf3b &( !A1 | !A0 ); C9 = gf3a9 |gf3b9; C8 = gf3a8 |gf3b8; C7 = gf3a7 |gf3b7; C6 = gf3a6 |gf3b6; C5 = gf3a5 |gf3b5; C4 = gf3a4 |gf3b4; C3 = gf3a3 |gf3b3; C2 = gf3a2 |gf3b2; C1 = gf3a1 |gf3b1; C0 = gf3a0 |gf3b0; enc_hc9 Input: A(8:0) Output: CW(9:0) if( !(A8&A7&A6&A5&A4&A3) ) { CW(9:0)= enc_hb9(hw); } else { if(!A2) CW(9:0)= enc_gb2(A(1:0)); if(A2&!A1) CW(9:0)= enc_gc1(A(0) ); if(A2& A1) CW(9:0)=!(enc_gc1(A(0))); } enc_gb2 Input: A1,A0 Output: C9,C8,C7,C6,C5,C4,C3,C2,C1,C0 C9= A0; C8=!A0; C7= A1; C6= A1; C5= A1; C4= A1; C3=!A1; C2=!A1; C1=!A1;  C0=!A1; enc_gc1 Input: A0 Output: C9,C8,C7,C6,C5,C4,C3,C2,C1,C0 C9= 1; C8= 1; C7= A0; C6= A0; C5= A0; C4= A0; C3=!A0; C2=!A0; C1=!A0; C0=!A0; enc_hc8 Input: A(7:0) Output: CW(9:0) if(!A7) CW(9:0)= !(enc_gc7(A(6:0))); if(A7&!A6) CW(9:0)= !(enc_gc6(A(5:0))); if(A7&A6) CW(9:0)= enc_ha6(A(5:0)); enc_hc6 Input: A(5:0) Output: CW(9:0) if(!A5) CW(9:0)= enc_ha5(A(4:0)); if(A5&!A4) CW(9:0)= !(enc_gc4(A(3:0))); if(A5& A4) CW(9:0)= enc_ha4(A(3:0)); enc_hd8 Input: A(7:0) Output: CW(9:0) if(!(A7&A6&A5)) CW(9:0)= enc_hc8(A(7:0)); else CW(9:0)= !(enc_gd5(A(4:0))); enc_hd7 Input: A(6:0) Output: CW(9:0) if(!A6) CW(9:0)= !(enc_gd6(A(5:0))); if(A6&!(A5&A4&A3)) CW(9:0)= enc_hc6(A(5:0)); if(A6& (A5&A4&A3)) CW(9:0)= !(enc_gd3(A(2:0))); HX Encoder Output Mux Input: ha8(9:0), ha6(9:0), ha5(9:0), ha4(9:0), hb9(9:0), hc9(9:0), hc8(9:0), hc6(9:0), hd8(9:0), hd7(9:0), h_sel(16:0) Output: hw(9:0) hb6(9:0) = ha6(9:0) hb5(9:0) = ha5(9:0) hb4(9:0) = ha4(9:0) hd9(9:0) = hc9(9:0) he9(9:0) =!hc9(9:0) he8(9:0) =!hc8(9:0) hf9(9:0) =!hb9(9:0) If(h_sel0) {hw(9:0)= ha8(9:0)  } If(h_sel1) {hw(9:0)= ha6(9:0)  } If(h_sel2) {hw(9:0)= ha5(9:0)  } If(h_sel3) {hw(9:0)= ha4(9:0)  } If(h_sel4) {hw(9:0)= hb9(9:0)  } If(h_sel5) {hw(9:0)= hb6(9:0)  } If(h_sel6) {hw(9:0)= hb5(9:0)  } If(h_sel7) {hw(9:0)= hb4(9:0)  } If(h_sel8) {hw(9:0)= hc9(9:0)  } If(h_sel9) {hw(9:0)= hc8(9:0)  } If(h_sel10) {hw(9:0)= hc6(9:0)  } If(h_sel11) {hw(9:0)= hd9(9:0)  } If(h_sel12) {hw(9:0)= hd8(9:0)  } If(h_sel13) {hw(9:0)= hd7(9:0)  } If(h_sel14) {hw(9:0)= he9(9:0)  } If(h_sel15) {hw(9:0)= he8(9:0)  } If(h_sel16) {hw(9:0)= hf9(9:0)  }

FIG. 10 illustrates a block diagram of encoder output circuit 266. Encoder output circuit 266 includes form code word circuit 330 and RDS calculator 332. Form code word circuit 334 combines the code words gw and hw received from the GX encoder and HX encoder, respectively, to form the code word. Also, if the state is negative, the entire code word is inversed to output the correct value. The output of form code word circuit 330 is sent to the communication channel 252 and RDS calculator 332. RDS calculator 332 receives the code word and the current state. RDS calculator 332 adds the values of the code word and the state to output the next state to the encoder input circuit 254, where it is used for a subsequent encoding. Encoder output circuit 266 operates according to calculations shown in Table 14. TABLE 14 Encoder Output Block Input: gw(9:0), hw(9:0), State(3:0) Output: W(19:0), NextState(3:0) Form Code Word if (State<=0) {W(19:10) = gw(9:0); W( 9: 0) = hw(9:0); } if (State>0) {W(19:10) =!gw(9:0); W( 9: 0) =!hw(9:0); } if( W(19:0)==0xAAAAA)  W(19:0) = 0x83EAA; if( W(19:0)==0x55555)    W(19:0) = 0x43D55; RDS Calculator HW=W19+W18+W17+W16+W15+W14+W13+W12+W11+W10+W9+W8+W7+W6+W5+W4+W3+W2+W1+W0 RDS = (2*HW)−20 NextState= State + RDS Note that Hamming weight(HW) of the code word W(19:0) is the sum of the 20 code bits. The running digital sum (RDS) of the code word is calculated by subtracting the number of “0” by the number of “1” in the code word. For example, if there are 13 “1” (HW=13) and number of “0” is (20−HW), the RDS is HW−(20−HW)= (2*HW)−20. In a sequence of code words, the cumulative RDS is the RDS of all bits from the beginning of the first code word to the end of the current code word. Note that the cumulative RDS in this design must be equal to either −4, −2, 0, 2 or 4. This number is also considered as the state of the encoder.

FIG. 11 illustrates a method 350 of decoding information received from communication channel 252. At step 352, the 20-bit code word is received from communication channel 252. Next, at step 354, the ‘g’ and ‘h’ bit segments from the code word are separated. At step 356, the ‘g’ 10-bit segment is decoded and at step 358 the ‘h’ 10-bit segment is decoded. Ultimately, at step 360, the 19-bit data word is formed and output.

FIG. 12 illustrates a decoder 370 that decodes information received from communication channel 252. Decoder 370 includes a decoder input circuit 372, a GX decoder 374, an HX decoder 376 and a decoder output circuit 378. As discussed in more detail below, the decoder input circuit 372 receives an initialization signal, the code word W_(19:0) and a word clock. The decoder input circuit 372 ascertains the state from the code word and separates the code word into a ‘g’ segment gcp_(9:0) and an ‘h’ segment hcp_(9:0). The ‘g’ segments and the ‘h’ segments are sent to the GX decoder 374 and HX decoder 376, respectively. The GX decoder 374 and the HX decoder 376 decode the respective segments and provide an output to decoder output circuit 378. The decoder output circuit 378 forms a 19-bit data word using the state value sent from decoder input 372 and outputs the 19-bit data word I_(18:0).

FIG. 13 illustrates a block diagram of decoder input circuit 372. Decoder input circuit 372 includes a state evaluator circuit 380, a state register 382, a 20-bit code word register 384 and an input mux 386. The initialization signal is sent to state evaluator circuit 380 and resets the state at the beginning of a first code word that is received from communication channel 252. The word clock initializes state register 382 and 20-bit code word register 384. The code word W_(19:0) is sent to the 20-bit code word register 384. The 20-bit code word is sent to state evaluator circuit 380 and input mux 386. Input mux 386 separates the 20-bit code word into a ‘g’ segment gcp and an ‘h’ segment hcp. Decoder input circuit 372 operates according to the calculations in Table 15. TABLE 15 Decoder Input Input:  W(19:0), Init, Word Clock Output: gcp(9:0), hcp(9:0), State(3:0) The Init signal is used to initialize Next State(3:0) to zero before the first clock signal. The rising edge of the Word Clock can be used to clock-in the 20-bit code word W(19:0) and shift the Next State to the State register. The State Evaluator is for calculating the Running Digital Sum (RDS) of the code word and the cumulative RDS. The RDS of the code word W(19:0) is:   RDS = (2*HW)−20  where HW is the Hamming weight of W(19:0)   Next State = State + RDS Therefore, the State represents the cumulative RDS of all code bits up till the end of the last code word. INPUT MUX if( wm(19:0)==0x83EAA) wm(19:0) = 0xAAAAA; if( wm(19:0)==0x43D55)   wm(19:0) = 0x55555; if(State<=0) {gcp(9:0)= wm(19:10); hcp(9:0)= wm(9:0); } if(State>0) {gcp(9:0)=!wm(19:10); hcp(9:0)=!wm(9:0); } ************************************************************************

FIG. 14 illustrates a block diagram of GX decoder 374. GX decoder 374 receives ‘g’ segment gcp from decoder input circuit 372. GX decoder 374 includes digital sum circuit 390, inverter 392, pattern select 394, a plurality of ‘g’ subgroup decoders 396 and a GX output mux 398. Digital sum calculator 390 determines the digital sum of ‘g’ segment gcp. If the digital sum of the ‘g’ segment gcp is less than zero, the inverter 392 will invert the ‘g’ segment gcp. After passing through inverter 392, a ‘g’ word gw is sent to the pattern generator 394 and plurality of ‘g’ subgroup decoders 396. Pattern selector 394 determines a 36-bit pattern based on the 10-bit word. This 36-bit pattern is used in each of the plurality of subgroup decoders 396 in order to determine the appropriate data value for the ‘g’ group word. Each of the plurality of subgroup decoders send a value indicative of the subgroup to GX output mux 398. GX output 398 sends the appropriate ‘g’ word gdw and ‘g’ type to decoder output circuit 378. Additionally, a value gm indicative of the ‘g’ type is sent to HX decoder 376 in order to select the appropriate ‘h’ word. GX decoder 374 operates according to the calculations in

FIG. 15 illustrates a block diagram of HX decoder 376. HX decoder 376 includes a first pattern generator 400, an inverter 402, a second pattern generator 404, a plurality of subgroup decoders 406 and an HX output mux 408. The first pattern generator 400 generates a 36-bit pattern based on the ‘h’ word hcp. Second pattern generator 404 generates a 36-bit pattern based on the inverse of ‘h’ word hcp. These values are provided to the plurality of subgroup decoders 406. The plurality of subgroup decoders 406 determine the appropriate values to be sent to HX output mux 408. Based on the gm and state values, the appropriate ‘h’ word hdw and ‘h’ type are sent to decoder output circuit 378. HX decoder 374 operates according to the calculations in Table 17. TABLE 17 HX Decoder Input: hcp(9:0), gm(3:0), State(3:0) Output: hdw(8:0), Htype(7:0) INV Input: hcp(9:0) Output: hwi(9:0) hwi(9:0) = !hcp(9:0) gen_p10 is the same as that in GX Decoder. dec_ha Input: hw(9:0),x(3:0),y(15:0),z(15:0) Output: hadw(8:0), haht(7:0) ( dec_gc, dec_gd, dec_ge and get_ds ) are identical to those in GX_Decoder Input Mux Input: gcdw(6:0),gddw(6:0),gedw(6:0),gcgt(7:0),gdgt(7:0),gegt(7:0), hds(4:0) Output: gdw(6:0), gt(7:0) if(hds=2) {gdw(6:0)=gcdw(6:0); gt(7:0)=gcgt(7:0); } if(hds=4) {gdw(6:0)=gddw(6:0); gt(7:0)=gdgt(7:0); } if(hds=6) {gdw(6:0)=gedw(6:0); gt(7:0)=gegt(7:0); } Output_ha Input: gdw(6:0), gt(7:0) Output: hdw(8:0), ht(7:0) if(gt=0x17) {hdw(8:0)=gdw(6:0); ht(7:0)=0x08; } if(gt=0x16) {hdw(8:0)=gdw(6:0)|0x80; ht(7:0)=0x08; } if(gt=0x26) {hdw(8:0)=gdw(6:0)|0xC0; ht(7:0)=0x08; } if(gt=0x25) {hdw(8:0)=gdw(6:0); ht(7:0)=0x06; } if(gt=0x35) {hdw(8:0)=gdw(6:0)|0x20; ht(7:0)=0x06; } if(gt=0x14) {hdw(8:0)=gdw(6:0); ht(7:0)=0x05; } if(gt=0x24) {hdw(8:0)=gdw(6:0)|0x10; ht(7:0)=0x05; } if(gt=0x23) {hdw(8:0)=gdw(6:0); ht(7:0)=0x04; } if(gt=0x33) {hdw(8:0)=gdw(6:0)|0x08; ht(7:0)=0x04; } Note: [hdw(8:0)=gdw(6:0)] means [hdw(8)=hdw(7)=0, hdw(6:0)=gdw(6:0)] dec_hb Input: hw(9:0),x(3:0),y(15:0),z(15:0) Output: hbdw(8:0), hbht(7:0) ( dec_gb, dec_gc, dec_gd, dec_ge, dec_gf and get_ds ) are identical to those in GX_Decoder Input Mux Input: gbdw(6:0), gcdw(6:0), gddw(6:0), gedw(6:0), gfdw(6:0), gbgt(7:0), gcgt(7:0), gdgt(7:0), gegt(7:0) gfgt(7:0), hds(4:0) Output: gdw(6:0), gt(7:0) if(hds=0) {gdw(6:0)=gbdw(6:0); gt(7:0)=gbgt(7:0); } if(hds=2) {gdw(6:0)=gcdw(6:0); gt(7:0)=gcgt(7:0); } if(hds=4) {gdw(6:0)=gddw(6:0); gt(7:0)=gdgt(7:0); } if(hds=6) {gdw(6:0)=gedw(6:0); gt(7:0)=gegt(7:0); } if(hds=8) {gdw(6:0)=gfdw(6:0); gt(7:0)=gfgt(7:0); } Output_hb Input: gdw(6:0), gt(7:0) Output: hdw(8.0), ht(7:0) if(gt=0x17) {hdw(8:0)=gdw(6:0); ht(7:0)=0x19; } if(gt=0x16) {hdw(8:0)=gdw(6:0)|0x80; ht(7:0)=0x19; } if(gt=0x26) {hdw(8:0)=gdw(6:0)|0xC0; ht(7:0)=0x19; } if(gt=0x07) {hdw(8:0)=gdw(6:0)|0x100; ht(7:0)=0x19; } if(gt=0x06) {hdw(8:0)=gdw(6:0)|0x180; ht(7:0)=0x19; } if(gt=0x05) {hdw(8:0)=gdw(6:0)|0x1C0; ht(7:0)=0x19; } if(gt=0x04) {hdw(8:0)=gdw(6:0)|0x1E0; ht(7:0)=0x19; } if(gt=0x03) {hdw(8:0)=gdw(6:0)|0x1F0; ht(7:0)=0x19; } if(gt=0x43) {hdw(8:0)=gdw(6:0)|0x1F8; ht(7:0)=0x19; } if(gt=0x25) {hdw(8:0)=gdw(6:0); ht(7:0)=0x16; } if(gt=0x35) {hdw(8:0)=gdw(6:0)|0x20; ht(7:0)=0x16; } if(gt=0x14) {hdw(8:0)=gdw(6:0); ht(7:0)=0x15; } if(gt=0x24) {hdw(8:0)=gdw(6:0)|0x10; ht(7:0)=0x15; } if(gt=0x23) {hdw(8:0)=gdw(6:0); ht(7:0)=0x14; } if(gt=0x33) {hdw(8:0)=gdw(6:0)|0x08; ht(7:0)=0x14; } Note: [hdw(8:0)=gdw(6:0)] means [hdw(8)=hdw(7)=0, hdw(6:0)=gdw(6:0)] dec_hc Input: hw(9:0), x(3:0),y(15:0),z(15:0), ihw(9:0), ix(3:0),iy(15:0),iz(15:0) Output: hcdw(8:0), hcht(7:0) Note that the 36-bit input ixyz is the combination of ix(3:0), iy(15:0) and iz(15:0). ( dec_gb, dec_gc, dec_gd, dec_ge and get_ds ) are identical to those in GX_Decoder Input Mux Input: igcdw(6:0), gbdw(6:0), gcdw(6:0), gddw(6:0), gedw(6:0), igcgt(7:0), gbgt(7:0), gcgt(7:0), gdgt(7:0), gegt(7:0), hds(4:0) Output: gdw(6:0), gt(7:0) if(hds=−2) {gdw(6:0)=igcdw(6:0); gt(7:0)=igcgt(7:0)|0x80; } if(hds=0) {gdw(6:0)=gbdw(6:0); gt(7:0)=gbgt(7:0); } if(hds=2) {gdw(6:0)=gcdw(6:0); gt(7:0)=gcgt(7:0); } if(hds=4) {gdw(6:0)=gddw(6:0); gt(7:0)=gdgt(7:0); } if(hds=6) {gdw(6:0)=gedw(6:0); gt(7:0)=gegt(7:0); } Output_hc Input: gdw(6:0), gt(7:0) Output: hdw(8:0), ht(7:0) if(gt=0x17) {hdw(8:0)=gdw(6:0); ht(7:0)=0x29; } if(gt=0x16) {hdw(8:0)=gdw(6:0)|0x80; ht(7:0)=0x29; } if(gt=0x26) {hdw(8:0)=gdw(6:0)|0xC0; ht(7:0)=0x29; } if(gt=0x07) {hdw(8:0)=gdw(6:0)|0x100; ht(7:0)=0x29; } if(gt=0x06) {hdw(8:0)=gdw(6:0)|0x180; ht(7:0)=0x29; } if(gt=0x05) {hdw(8:0)=gdw(6:0)|0x1C0; ht(7:0)=0x29; } if(gt=0x04) {hdw(8:0)=gdw(6:0)|0x1E0; ht(7:0)=0x29; } if(gt=0x03) {hdw(8:0)=gdw(6:0)|0x1F0; ht(7:0)=0x29; } if(gt=0x02) {hdw(8:0)=gdw(6:0)|0x1F8; ht(7:0)=0x29; } if(gt=0x11) {hdw(8:0)=gdw(6:0)|0x1FC; ht(7:0)=0x29; } if(gt=0x91) {hdw(8:0)=gdw(6:0)|0x1FE; ht(7:0)=0x29; } if(gt=0x97) {hdw(8:0)=gdw(6:0); ht(7:0)=0x28; } if(gt=0x96) {hdw(8:0)=gdw(6:0)|0x80; ht(7:0)=0x28; } if(gt=0x25) {hdw(8:0)=gdw(6:0)|0xC0; ht(7:0)=0x28; } if(gt=0x35) {hdw(8:0)=gdw(6:0)|0xE0; ht(7:0)=0x28; } if(gt=0x14) {hdw(8:0)=gdw(6:0); ht(7:0)=0x26; } if(gt=0x24) {hdw(8:0)=gdw(6:0)|0x10; ht(7:0)=0x26; } if(gt=0x94) {hdw(8:0)=gdw(6:0)|0x20; ht(7:0)=0x26; } if(gt=0x23) {hdw(8:0)=gdw(6:0)|0x30; ht(7:0)=0x26; } if(gt=0x33) {hdw(8:0)=gdw(6:0)|0x38; ht(7:0)=0x26; } Note: [hdw(8:0)=gdw(6:0)] means [hdw(8)=hdw(7)=0, hdw(6:0)=gdw(6:0)] dec_hd Input: hw(9:0), x(3:0),y(15:0),z(15:0), ihw(9:0), ix(3:0),iy(15:0), iz(15:0) Output: hddw(8:0), hdht(7:0) ( dec_gb, dec_gc, dec_gd and get_ds ) are identical to those in GX_Decoder Output of the INV block is the bitwise inverse of its input. Input Mux Input: igddw(6:0), igcdw(6:0), gbdw(6:0), gcdw(6:0), gddw(6:0), igdgt(7:0), igcgt(7:0), gbgt(7:0), gcgt(7:0), gdgt(7:0), hds(4:0) Output: gdw(6:0), gt(7:0) if(hds=−4) {gdw(6:0)=igddw(6:0); gt(7:0)=igdgt(7:0)|0x80; } if(hds=−2) {gdw(6:0)=igcdw(6:0); gt(7:0)=igcgt(7:0)|0x80; } if(hds=0) {gdw(6:0)=gbdw(6:0); gt(7:0)=gbgt(7:0); } if(hds=2) {gdw(6:0)=gcdw(6:0); gt(7:0)=gcgt(7:0); } if(hds=4) {gdw(6:0)=gddw(6:0); gt(7:0)=gdgt(7:0); } Output_hd Input: gdw(6:0), gt(7:0) Output: hdw(8:0), ht(7:0) if(gt=0x17) {hdw(8:0)=gdw(6:0); ht(7:0)=0x39; } if(gt=0x16) {hdw(8:0)=gdw(6:0)|0x80; ht(7:0)=0x39; } if(gt=0x26) {hdw(8:0)=gdw(6:0)|0xC0; ht(7:0)=0x39; } if(gt=0x07) {hdw(8:0)=gdw(6:0)|0x100; ht(7:0)=0x39; } if(gt=0x06) {hdw(8:0)=gdw(6:0)|0x180; ht(7:0)=0x39; } if(gt=0x05) {hdw(8:0)=gdw(6:0)|0x1C0; ht(7:0)=0x39; } if(gt=0x04) {hdw(8:0)=gdw(6:0)|0x1E0; ht(7:0)=0x39; } if(gt=0x03) {hdw(8:0)=gdw(6:0)|0x1F0; ht(7:0)=0x39; } if(gt=0x02) {hdw(8:0)=gdw(6:0)|0x1F8; ht(7:0)=0x39; } if(gt=0x11) {hdw(8:0)=gdw(6:0)|0x1FC; ht(7:0)=0x39; } if(gt=0x91) {hdw(8:0)=gdw(6:0)|0x1FE; ht(7:0)=0x39; } if(gt=0x97) {hdw(8:0)=gdw(6:0); ht(7:0)=0x38; } if(gt=0x96) {hdw(8:0)=gdw(6:0)|0x80; ht(7:0)=0x38; } if(gt=0x25) {hdw(8:0)=gdw(6:0)|0xC0; ht(7:0)=0x38; } if(gt=0xA5) {hdw(8:0)=gdw(6:0)|0xE0; ht(7:0)=0x38; } if(gt=0xA6) {hdw(8:0)=gdw(6:0); ht(7:0)=0x37; } if(gt=0x14) {hdw(8:0)=gdw(6:0)|0x40; ht(7:0)=0x37; } if(gt=0x24) {hdw(8:0)=gdw(6:0)|0x50; ht(7:0)=0x37; } if(gt=0x94) {hdw(8:0)=gdw(6:0)|0x60; ht(7:0)=0x37; } if(gt=0x23) {hdw(8:0)=gdw(6:0)|0x70; ht(7:0)=0x37; } if(gt=0xA3) {hdw(8:0)=gdw(6:0)|0x78; ht(7:0)=0x37; } dec_he Input: hw(9:0), x(3:0),y(15:0),z(15:0), ihw(9:0), ix(3:0),iy(15:0), iz(15:0) Output: hedw(8:0), heht(7:0) Description of Block dec_hc is shown before. Since patterns of group “he” are the inverse of group “hc”, dec_he is same as dec_hc with the input inverted. Note here that input hw of dec_he is used as input ihw of dec_hc and input ihw of dec_he is used as input hw of dec_hc. Similarly, xyz of dec_he is connected to ixyz of dec_hc and vice versa. hedw(8:0) = hdw(8:0) of dec_hc Modify ht heht(7:4) = [0,1,0,0] heht(3:0) = ht(3:0) of ht from dec_hc dec_hf Input: ihw(9:0), ix(3:0),iy(15:0),iz(15:0) Output: hfdw(8:0), hfht(7:0) Description of Block dec_hb is shown before. Since patterns of group “hf” are the inverse of group “hb”, dec_hf is same as dec_hb with the input inverted. Note that input ihw of dec_hf is used as input hw of dec_hb. Similarly, ixyz of dec_hf is connected to xyz of dec_hb. hfdw(8:0) = hdw(8:0) of dec_hb Modify ht hfht(7:4) = [0,1,0,1] hfht(3:0) = ht(3:0) of ht from dec_hb HX Output Mux Input: hadw(7:0), hbdw(8:0), hcdw(8:0), hddw(8:0), hedw(8:0),  hfdw(8:0), haht(7:0), hbht(7:0), hcht(7:0), hdht(7:0), heht(7:0),  hfht(7:0), gm(3:0), State(3:0) Output: hdw(8:0), Htype(7:0) If(State< −4) State=−4; If(State> 4) State= 4; If(State= −4 or State= 4) { if(gm=9) {hdw(8:0)=hadw(8:0); Htype(7:0)=haht(7:0); } if(gm=0) {hdw(8:0)=hbdw(8:0); Htype(7:0)=hbht(7:0); } if(gm=1) {hdw(8:0)=hcdw(8:0); Htype(7:0)=hcht(7:0); } if(gm=2) {hdw(8:0)=hddw(8:0); Htype(7:0)=hdht(7:0); } if(gm=3) {hdw(8:0)=hedw(8:0); Htype(7:0)=heht(7:0); } } If(State= −2 or State= 2) { if(gm=9) {hdw(8:0)=hbdw(8:0); Htype(7:0)=hbht(7:0); } if(gm=0) {hdw(8:0)=hcdw(8:0); Htype(7:0)=hcht(7:0); } if(gm=1) {hdw(8:0)=hddw(8:0); Htype(7:0)=hdht(7:0); } if(gm=2) {hdw(8:0)=hedw(8:0); Htype(7:0)=heht(7:0); } if(gm=3) {hdw(8:0)=hfdw(8:0); Htype(7:0)=hfht(7:0); } } If(State= 0) { if(gm=9) {hdw(8:0)=hcdw(8:0); Htype(7:0)=hcht(7:0); } if(gm=0) {hdw(8:0)=hddw(8:0); Htype(7:0)=hdht(7:0); } if(gm=1) {hdw(8:0)=hedw(8:0); Htype(7:0)=heht(7:0); } if(gm=2) {hdw(8:0)=hfdw(8:0); Htype(7:0)=hfht(7:0); } }

FIG. 16 illustrates a block diagram of decoder output circuit 378. Decoder output circuit 378 includes a form 19-bit data word circuit 410. The data word circuit 410 receives the ‘g’ word gdw, and ‘h’ word hdw, ‘g’ type, ‘h’ type and state. Using calculations, the data word circuit 410 outputs the user data word I_(18:0). The operation of decoder output circuit 378 is performed according to the calculations in Table 18. TABLE 18 Decoder Output Input: gdw(6:0), hdw(8:0), Gtype(7:0),Htype(7:0), State(3:0) Output: I(18:0) if(State==−4 or 4) { if( (gt==0x07)&&(ht==0x19) ) {I(18:16)=[0,0,0];   I(15:9)=gdw(6:0); I(8:0)=hdw(8:0); } if( (gt==0x17)&&(ht==0x29) ) {I(18:16)=[0,0,1];   I(15:9)=gdw(6:0); I(8:0)=hdw(8:0); } if( (gt==0x97)&&(ht==0x08) ) {I(18:15)=[0,1,0,0];   I(14:8)=gdw(6:0); I(7:0)=hdw(7:0); } if( (gt==0x06)&&(ht==0x19) ) {I(18:15)=[0,1,0,1];   I(14:9)=gdw(5:0); I(8:0)=hdw(8:0); } if( (gt==0x17)&&(ht==0x28) ) {I(18:15)=[0,1,1,0];   I(14:8)=gdw(6:0); I(7:0)=hdw(7:0); } if( (gt==0x16)&&(ht==0x29) ) {I(18:15)=[0,1,1,1];   I(14:9)=gdw(5:0); I(8:0)=hdw(8:0); } if( (gt==0x26)&&(ht==0x39) ) {I(18:15)=[1,0,0,0];   I(14:9)=gdw(5:0); I(8:0)=hdw(8:0); } if( (gt==0x96)&&(ht==0x08) ) {I(18:14)=[1,0,0,1,0];   I(13:8)=gdw(5:0); I(7:0)=hdw(7:0); } if( (gt==0x05)&&(ht==0x19) ) {I(18:14)=[1,0,0,1,1];   I(13:9)=gdw(4:0); I(8:0)=hdw(8:0); } if( (gt==0x16)&&(ht==0x28) ) {I(18:14)=[1,0,1,0,0];   I(13:8)=gdw(5:0); I(7:0)=hdw(7:0); } if( (gt==0x26)&&(ht==0x38) ) {I(18:14)=[1,0,1,0,1];   I(13:8)=gdw(5:0); I(7:0)=hdw(7:0); } if( (gt==0x25)&&(ht==0x39) ) {I(18:14)=[1,0,1,1,0];   I(13:9)=gdw(4:0); I(8:0)=hdw(8:0); } if( (gt==0x35)&&(ht==0x49) ) {I(18:14)=[1,0,1,1,1];   I(13:9)=gdw(4:0); I(8:0)=hdw(8:0); } if( (gt==0x97)&&(ht==0x06) ) {I(18:13)=[1,1,0,0,0,0];   I(12:6)=gdw(6:0); I(5:0)=hdw(5:0); } if( (gt==0x07)&&(ht==0x16) ) {I(18:13)=[1,1,0,0,0,1];   I(12:6)=gdw(6:0); I(5:0)=hdw(5:0); } if( (gt==0x04)&&(ht==0x19) ) {I(18:13)=[1,1,0,0,1,0];   I(12:9)=gdw(3:0); I(8:0)=hdw(8:0); } if( (gt==0x17)&&(ht==0x26) ) {I(18:13)=[1,1,0,0,1,1];   I(12:6)=gdw(6:0); I(5:0)=hdw(5:0); } if( (gt==0x14)&&(ht==0x29) ) {I(18:13)=[1,1,0,1,0,0];   I(12:9)=gdw(3:0); I(8:0)=hdw(8:0); } if( (gt==0x26)&&(ht==0x37) ) {I(18:13)=[1,1,0,1,0,1];   I(12:7)=gdw(5:0); I(6:0)=hdw(6:0); } if( (gt==0x25)&&(ht==0x38) ) {I(18:13)=[1,1,0,1,1,0];   I(12:8)=gdw(4:0); I(7:0)=hdw(7:0); } if( (gt==0x24)&&(ht==0x39) ) {I(18:13)=[1,1,0,1,1,1];   I(12:9)=gdw(3:0); I(8:0)=hdw(8:0); } if( (gt==0x35)&&(ht==0x48) ) {I(18:13)=[1,1,1,0,0,0];   I(12:8)=gdw(4:0); I(7:0)=hdw(7:0); } if( (gt==0x97)&&(ht==0x05) ) {I(18:12)=[1,1,1,0,0,1,0];   I(11:5)=gdw(6:0); I(4:0)=hdw(4:0); } if( (gt==0x96)&&(ht==0x06) ) {I(18:12)=[1,1,1,0,0,1,1];   I(11:6)=gdw(5:0); I(5:0)=hdw(5:0); } if( (gt==0x07)&&(ht==0x15) ) {I(18:12)=[1,1,1,0,1,0,0];   I(11:5)=gdw(6:0); I(4:0)=hdw(4:0); } if( (gt==0x06)&&(ht==0x16) ) {I(18:12)=[1,1,1,0,1,0,1];   I(11:6)=gdw(5:0); I(5:0)=hdw(5:0); } if( (gt==0x03)&&(ht==0x19) ) {I(18:12)=[1,1,1,0,1,1,0];   I(11:9)=gdw(2:0); I(8:0)=hdw(8:0); } if( (gt==0x16)&&(ht==0x26) ) {I(18:12)=[1,1,1,0,1,1,1];   I(11:6)=gdw(5:0); I(5:0)=hdw(5:0); } if( (gt==0x14)&&(ht==0x28) ) {I(18:12)=[1,1,1,1,0,0,0];   I(11:8)=gdw(3:0); I(5:0)=hdw(5:0); } if( (gt==0x25)&&(ht==0x37) ) {I(18:12)=[1,1,1,1,0,0,1];   I(11:7)=gdw(4:0); I(6:0)=hdw(6:0); } if( (gt==0x24)&&(ht==0x38) ) {I(18:12)=[1,1,1,1,0,1,0];   I(11:8)=gdw(3:0); I(7:0)=hdw(7:0); } if( (gt==0x23)&&(ht==0x39) ) {I(18:12)=[1,1,1,1,0,1,1];   I(11:9)=gdw(2:0); I(8:0)=hdw(8:0); } if( (gt==0x33)&&(ht==0x49) ) {I(18:12)=[1,1,1,1,1,0,0];   I(11:9)=gdw(2:0); I(8:0)=hdw(8:0); } if( (gt==0x97)&&(ht==0x04) ) {I(18:11)=[1,1,1,1,1,0,1,0];   I(10:4)=gdw(6:0); I(3:0)=hdw(3:0); } if( (gt==0x96)&&(ht==0x05) ) {I(18:11)=[1,1,1,1,1,0,1,1];   I(10:5)=gdw(5:0); I(4:0)=hdw(4:0); } if( (gt==0x07)&&(ht==0x14) ) {I(18:11)=[1,1,1,1,1,1,0,0];   I(10:4)=gdw(6:0); I(3:0)=hdw(3:0); } if( (gt==0x06)&&(ht==0x15) ) {I(18:11)=[1,1,1,1,1,1,0,1];   I(10:5)=gdw(5:0); I(4:0)=hdw(4:0); } if( (gt==0x05)&&(ht==0x16) ) {I(18:11)=[1,1,1,1,1,1,1,0];   I(10:6)=gdw(4:0); I(5:0)=hdw(5:0); } if( (gt==0x24)&&(ht==0x37) ) {I(18:11)=[1,1,1,1,1,1,1,1];   I(10:7)=gdw(3:0); I(6:0)=hdw(6:0); } } if(State==−2 or 2) { if( (gt==0x97)&&(ht==0x19) ) {I(18:16)=[0,0,0];   I(15:9)=gdw(6:0); I(8:0)=hdw(8:0); } if( (gt==0x07)&&(ht==0x29) ) {I(18:16)=[0,0,1];   I(15:9)=gdw(6:0); I(8:0)=hdw(8:0); } if( (gt==0x17)&&(ht==0x39) ) {I(18:16)=[0,1,0];   I(15:9)=gdw(6:0); I(8:0)=hdw(8:0); } if( (gt==0x96)&&(ht==0x19) ) {I(18:15)=[0,1,1,0];   I(14:9)=gdw(5:0); I(8:0)=hdw(8:0); } if( (gt==0x07)&&(ht==0x28) ) {I(18:15)=[0,1,1,1];   I(14:8)=gdw(6:0); I(7:0)=hdw(7:0); } if( (gt==0x06)&&(ht==0x29) ) {I(18:15)=[1,0,0,0];   I(14:9)=gdw(5:0); I(8:0)=hdw(8:0); } if( (gt==0x17)&&(ht==0x38) ) {I(18:15)=[1,0,0,1];   I(14:8)=gdw(6:0); I(7:0)=hdw(7:0); } if( (gt==0x16)&&(ht==0x39) ) {I(18:15)=[1,0,1,0];   I(14:9)=gdw(5:0); I(8:0)=hdw(8:0); } if( (gt==0x26)&&(ht==0x49) ) {I(18:15)=[1,0,1,1];   I(14:9)=gdw(5:0); I(8:0)=hdw(8:0); } if( (gt==0x06)&&(ht==0x28) ) {I(18:14)=[1,1,0,0,0];   I(13:8)=gdw(5:0); I(7:0)=hdw(7:0); } if( (gt==0x05)&&(ht==0x29) ) {I(18:14)=[1,1,0,0,1];   I(13:9)=gdw(4:0); I(8:0)=hdw(8:0); } if( (gt==0x17)&&(ht==0x37) ) {I(18:14)=[1,1,0,1,0];   I(13:7)=gdw(6:0); I(6:0)=hdw(6:0); } if( (gt==0x16)&&(ht==0x38) ) {I(18:14)=[1,1,0,1,1];   I(13:8)=gdw(5:0); I(7:0)=hdw(7:0); } if( (gt==0x26)&&(ht==0x48) ) {I(18:14)=[1,1,1,0,0];   I(13:8)=gdw(5:0); I(7:0)=hdw(7:0); } if( (gt==0x35)&&(ht==0x59) ) {I(18:14)=[1,1,1,0,1];   I(13:9)=gdw(4:0); I(8:0)=hdw(8:0); } if( (gt==0x97)&&(ht==0x16) ) {I(18:13)=[1,1,1,1,0,0];   I(12:6)=gdw(6:0); I(5:0)=hdw(5:0); } if( (gt==0x07)&&(ht==0x26) ) {I(18:13)=[1,1,1,1,0,1];   I(12:6)=gdw(6:0); I(5:0)=hdw(5:0); } if( (gt==0x05)&&(ht==0x28) ) {I(18:13)=[1,1,1,1,1,0];   I(12:8)=gdw(4:0); I(7:0)=hdw(7:0); } if( (gt==0x04)&&(ht==0x29) ) {I(18:13)=[1,1,1,1,1,1];   I(12:9)=gdw(3:0); I(8:0)=hdw(8:0); } } if(State==0) { if( (gt==0x97)&&(ht==0x29) ) {I(18:16)=[0,0,0];   I(15:9)=gdw(6:0); I(8:0)=hdw(8:0); } if( (gt==0x07)&&(ht==0x39) ) {I(18:16)=[0,0,1];   I(15:9)=gdw(6:0); I(8:0)=hdw(8:0); } if( (gt==0x17)&&(ht==0x49) ) {I(18:16)=[0,1,0];   I(15:9)=gdw(6:0); I(8:0)=hdw(8:0); } if( (gt==0x97)&&(ht==0x28) ) {I(18:15)=[0,1,1,0];   I(14:8)=gdw(6:0); I(7:0)=hdw(7:0); } if( (gt==0x96)&&(ht==0x29) ) {I(18:15)=[0,1,1,1];   I(14:9)=gdw(5:0); I(8:0)=hdw(8:0); } if( (gt==0x07)&&(ht==0x38) ) {I(18:15)=[1,0,0,0];   I(14:8)=gdw(6:0); I(7:0)=hdw(7:0); } if( (gt==0x06)&&(ht==0x39) ) {I(18:15)=[1,0,0,1];   I(14:9)=gdw(5:0); I(8:0)=hdw(8:0); } if( (gt==0x17)&&(ht==0x48) ) {I(18:15)=[1,0,1,0];   I(14:8)=gdw(6:0); I(7:0)=hdw(7:0); } if( (gt==0x16)&&(ht==0x49) ) {I(18:15)=[1,0,1,1];   I(14:9)=gdw(5:0); I(8:0)=hdw(8:0); } if( (gt==0x26)&&(ht==0x59) ) {I(18:15)=[1,1,0,0];   I(14:9)=gdw(5:0); I(8:0)=hdw(8:0); } if( (gt==0x96)&&(ht==0x28) ) {I(18:14)=[1,1,0,1,0];   I(13:8)=gdw(5:0); I(7:0)=hdw(7:0); } if( (gt==0x07)&&(ht==0x37) ) {I(18:14)=[1,1,0,1,1];   I(13:7)=gdw(6:0); I(6:0)=hdw(6:0); } if( (gt==0x06)&&(ht==0x38) ) {I(18:14)=[1,1,1,0,0];   I(13:8)=gdw(5:0); I(7:0)=hdw(7:0); } if( (gt==0x05)&&(ht==0x39) ) {I(18:14)=[1,1,1,0,1];   I(13:9)=gdw(4:0); I(8:0)=hdw(8:0); } if( (gt==0x16)&&(ht==0x48) ) {I(18:14)=[1,1,1,1,0];   I(13:8)=gdw(5:0); I(7:0)=hdw(7:0); } if( (gt==0x25)&&(ht==0x59) ) {I(18:14)=[1,1,1,1,1];   I(13:9)=gdw(4:0); I(8:0)=hdw(8:0); } }

In summary, a method (200) of encoding digital information in a system is provided. The method (200) includes receiving (202) a sequence of user bits and calculating (204) a running digital sum (RDS) of the system. In addition, a code word is generated (214) based on the sequence of user bits and the RDS of the system to maintain the RDS of the system calculated with the code word to within a selected range.

Another embodiment of the present invention relates to a system (100, 250) for generating a code word from a sequence of user bits. The system (100, 250) has an input circuit (254) adapted to receive the sequence of user bits and a calculation circuit (332) adapted to calculate the running digital sum (RDS) of the system. An encoder (250) is also provide that is adapted to generate a code word based on the sequence of user bits and the RDS of the system to maintain the RDS of the system calculated with the code word to within a selected range.

It is to be understood that even though numerous characteristics and advantages of various embodiments of the invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the particular application for the communication system while maintaining substantially the same functionality without departing from the scope and spirit of the present invention. In addition, although the preferred embodiment described herein is directed to a coding system for a disc drive, it will be appreciated by those skilled in the art that the teachings of the present invention can be applied to system such as satellite communications and cellular phones, without departing from the scope and spirit of the present invention. 

1. A codeword for use in a communication channel, comprising: a first segment comprising a plurality of bits having a running digital sum (RDS); and a second segment comprising a plurality of bits based on the RDS of the first segment.
 2. The codeword of claim 1 wherein the communication channel is in a system having a running digital sum (RDS) based on previous bits in the system and wherein the codeword has a bit pattern representing a user data word and the RDS of the system.
 3. The codeword of claim 1 wherein the first segment has a bit pattern representing an encoded fragment of a user data word.
 4. The codeword of claim 1 the second segment has a bit pattern representing an encoded fragment of a user data word.
 5. The codeword of claim 1 wherein the first segment has a bit pattern representing a first encoded fragment of a user data word and the second segment of has a bit pattern representing a second encoded fragment of a user data word.
 6. The codeword of claim 1 wherein the first segment is 10 bits and the second segment is 10 bits.
 7. A codeword representing an encoded user data word for use in a system, the codeword comprising: a first segment representing a first fragment of the user data word; and a second segment representing a second fragment of the user data word, wherein the first and second segments represent a state value for the system.
 8. The codeword of claim 7 wherein the second segment has a bit pattern based on a running digital sum of the first segment.
 9. The codeword of claim 7 wherein the first segment is 10 bits and the second segment is 10 bits.
 10. The codeword of claim 9 wherein the encoded user data word is 19 bits. 